Portal 2

Portal 2
Portal 2 retail cover art. The co-op campaign robot characters Atlas (bottom) and P-Body are featured
Developer(s)	Valve Corporation
Publisher(s)	Valve Corporation
Director(s)	Joshua Weier
Producer(s)	Gabe Newell
Artist(s)	Jeremy Bennett Randy Lundeen (art directors)
Writer(s)	Erik Wolpaw Jay Pinkerton
Composer(s)	Mike Morasky Jonathan Coulton (song)
Series	Portal
Engine	Source
Platform(s)	Microsoft Windows, Mac OS X, Xbox 360, PlayStation 3
Release	'Retail'Steam INT: April 19, 2011
Genre(s)	Puzzle-platform game Science fiction
Mode(s)	Single-player, cooperative

Portal 2 is a first-person puzzle-platform video game developed by Valve Corporation. It is the sequel to the 2007 video game Portal and was announced on March 5, 2010, following a week-long alternate reality game based on new patches to the original game. Though initially slated for release in the last quarter of 2010, the game was postponed to the week of April 18, 2011. The game was released by Valve through Steam for Microsoft Windows and Mac OS X, while the PlayStation 3, Xbox 360 and retail Windows/OS X versions of the game are distributed by Electronic Arts. The game's release on Steam was preceded by a second multi-week alternate reality game, the Potato Sack, involving 13 independently-developed titles, culminating in a distributed computing spoof to release Portal 2 several hours early.

Portal 2 comprises a series of puzzles that must be solved by teleporting the player's character and simple objects using the "portal gun", a device that can create inter-spatial portals between flat planes. The game's unique physics allow momentum to be retained through portals, requiring creative use of portals to maneuver through the test chambers. Other gameplay elements were added to Portal 2, including tractor beams, laser redirection, and special paint-like gels that impart special properties to objects they touch, an idea taken from the Independent Games Festival-winning DigiPen student project Tag: The Power of Paint.

Within the single player campaign, the player returns as the human Chell, having awakened from stasis after several hundred years. Chell must navigate the dilapidated Aperture Science Enrichment Center and its test chambers with the portal gun while the facility is rebuilt by the reactivated GLaDOS, a rampant artificially intelligent computer. With a larger story, Valve introduced additional characters, including Wheatley, voiced by Stephen Merchant, and recordings of Aperture Science CEO Cave Johnson, voiced by J.K. Simmons. Ellen McLain returns to voice GLaDOS. Additional music from Jonathan Coulton and The National appear in the game. Portal 2 also includes a two-player co-operative mode in which the player-characters, the robots Atlas and P-body, must work together to complete each test chamber using their own individual portal guns.

Though many reviewers were concerned about the difficulty of expanding Portal into a full sequel, critics universally praised Portal 2. The game's writing, pacing, and comedy were highlighted as stand-out elements, with critics applauding the voice work of McLain, Merchant, and Simmons. Reviews also highlighted the new gameplay elements, the game's challenging but surmountable learning curve, and the addition of the co-operative mode.

Gameplay

Portal 2 continues to challenge players to use portals to traverse rooms in unusual manners, such as flinging, in which the player uses the magnitude of the momentum gained by gravitational acceleration through the blue portal to cross a wide gap out of the orange portal.

See also: Gameplay in Portal

Portal 2 is a puzzle game presented from the first-person perspective. Normally, the player, as either Chell in the single-player campaign or as one of two robots, Atlas or P-body, in the co-operative campaign, can move, look, and carry and drop objects. The goal is to maneuver the characters through a number of test chambers in the Aperture Science facility, traversing the chamber from the start to the exit. Though the player-character can take some damage for a brief period of time, they will die under sustained injury and be restarted at a recent checkpoint; however, characters are equipped with "long fall boots" that absorb the shock of landing after a large vertical drop. The player must figure out how to overcome seemingly-bottomless gaps, evade pools of toxic liquid, or avoid line-of-sight or even disable robotic turrets to safely arrive at the exit.

Initial levels provide a tutorial on general movement controls and interactions with the environment. After these levels, the player will be required to solve puzzles in test chambers within the Aperture Science Enrichment Center using the "portal gun" (the Aperture Science Handheld Portal Device), a device that can create two portals connecting two surfaces across space. Players solve puzzles by using these portals to move unconventionally between rooms or to use the ability to fling objects or themselves across a distance. The functionality of the gun has not changed between the games, but within Portal 2, players can take advantage of the bleeding of other physical effects through the portals. One example is the direction of Excursion Funnel tractor beams or Hard Light Bridges through portals to provide surfaces or areas which the player can use to move the player-character or specific objects across obstacles. While early technology demonstrations included the use of Pneumatic Diversity Vents, a series of transport pneumatic tubes, and the interaction of their suction or venting power through portals, these do not appear in the final game.

The game also introduces special paint-like gels that can be used to impart certain physical effects to a surface such as Propulsion Gel that boosts Chell's speed as she crosses a surface, and Repulsion Gel that allows her to jump from a surface. A third gel type, Conversion Gel, allows any surface coated with it to accept portals. The player will be required to determine how to transport that gel to appropriate surfaces using portals in order to progress. The gels can also be applied to objects, such as the Weighted Storage Cube crates, that affect their own physical nature. Water can be redirected to wash away gels applied by the player, returning the surface or object to its normal state. In addition to the Storage Cube, there are new types of objects that assist the player, including Redirection Cubes with mirrored, reflective surfaces used to redirect Thermal Discouragement laser beams, Aerial Faith Plates that can launch objects placed on them, and spherical Weighted Storage Balls, which made a brief appearance in the original game in one of the advanced chambers. The heart-decorated Weighted Companion Cube, used by GLaDOS in the first game to make Chell form an emotional bond to the inanimate object before incinerating it, also appears in the sequel.

While most of the single-player game takes place in the test chambers created by GLaDOS or her personality cores, there are times where the player will need to move behind-the-scenes in areas beyond the test chambers as they are reconfigured, leaving the player free of GLaDOS's observation and control.

The game includes a two-player co-operative mode in addition to the single player mode. This mode can be played by two players at the same computer/console via split-screen, or through two remote players at their own computer/consoles; Microsoft Windows, MacOS X, and PlayStation 3 users can play with each other regardless of platform. Both players control separate portal guns and can use the other player's portals as necessary; each player's portals are of a different color scheme (blue/purple, and orange/red) to help distinguish between the two sets. Because of the number of possible portal combinations, the test chambers that the players proceed through are much more difficult than the single-player campaign, requiring the two players to work together. Initial chambers set each robot in their own separate section of the chamber, and their solutions teach the use of the communication tools and portal use to complete. Latter chambers are less structured, and require the players to use both sets of portals for laser or funnel redirection, launches, or other maneuvers to reach the exit. Should either robot die, a new robot will be recreated shortly after, allowing players to continue on the puzzle without restarting. The game includes voice communication between players for this mode as well as split-screen for players playing locally. Online players have the ability to temporarily enter a split-screen view to help coordinate actions. Players have the ability to "ping" walls or objects on the game's levels as a means of informing the other player what they need to do, starting countdown timers for concerted actions, and perform emotes with their partner, such as waving or hugging. Borrowing on the concept from Left 4 Dead, players, both in the co-op and single player campaign, can see the outlines of placed portals through walls and other obstacles to identify their locations. The game tracks what chamber each player has completed, and allow a player to replay chambers they have completed with other partners who may have not yet completed that chamber.

Valve has stated that both the single player and the co-operative campaigns are about each 2 to 2.5 times as long as the original campaign in Portal, with the overall game five times longer than the original. Erik Wolpaw estimates each campaign is about six hours long.

As with previous Valve games, Portal 2 contains in-game commentary from the game developers, writers, and artists. The commentary, accessed after completing the game once, appears on node icons scattered through the game's levels, either where the development team found significant changes from their original ideas, or where ideas failed to work out for the game.

Plot

Portal 2 follows the player-character Chell's fate after the end of Portal. Retroactively patched just prior to the sequel's official announcement, the ending of the first game shows Chell being dragged away from the remains of GLaDOS by an unseen figure with a robotic voice, later identified by writer Erik Wolpaw as the "Party Escort Bot". She is placed in stasis within Aperture Science for a period of many years, during which the facility becomes overrrun by decay and nature. The Aperture setting is part of the Half-Life series; while Portal's events occurred before Half-Life 2, the sequel takes place much later than that game. One hidden area of the game shows the former location of Aperture Science's cargo ship, the Borealis, in the bowels of the facility; this ship is mentioned as part the Half-Life universe at the end of Episode 2, having been discovered in the Arctic, situated in a seemingly-impossible position with all hands lost. Portal 2 suggests the ship was related as a result of an experimental teleportation device being developed by Aperture to compete with Black Mesa Research Facility, a competitor featured in Half-Life.

Main campaign

Chell wakes to find herself in what appears to be a motel room. A robotic voice guides her through a cognitive test before she is put back to sleep. When she next awakes, many years have passed. Wheatley (Stephen Merchant), a personality core, moves the room—located in one of hundreds of shipping containers among a giant warehouse—helping her to escape through the test chambers of the Aperture Science facility. Wheatley has become concerned about the state of decay and seeks to correct it, guiding Chell through the test chambers to the dormant GLaDOS (Ellen McLain). While attempting to activate an escape pod, they accidentally wake her. GLaDOS has not forgiven Chell for "murdering" her years ago, and begins rebuilding the ruined facility to put Chell through more tests, stating, "I think we can put our differences behind us... for science... you monster."

With Wheatley's help, Chell is able to escape the test chambers and disable the neurotoxin and turret manufacturing plants. When they confront GLaDOS a second time, Chell is able to exchange Wheatley's personality for GLaDOS's. Wheatley becomes intoxicated with power and places GLaDOS's personality into a module powered by a potato battery; this form of the AI is nicknamed "POTaTOS" within the developer commentary. He betrays Chell and sends both Chell and GLaDOS miles deep into the bowels of the facility. As they fall, GLaDOS chastises Chell for putting Wheatley in the position of power, claiming that he was "the product of the greatest minds of a generation working together with the express purpose of building the dumbest moron who ever lived", designed to hamper GLaDOS's decision-making processes.

After landing, GLaDOS is abducted by a bird, while Chell works to climb back to the higher levels through a series of chambers automated by recordings of Aperture Science's CEO, Cave Johnson (J. K. Simmons). During her climb through the various strata of old Aperture test chambers, Chell learns from the recordings that Johnson became increasingly deranged over time. His assistant, Caroline (McLain), would eventually be a test subject for a mind-to-computer transfer system and be placed in charge of the facility, ultimately becoming part of GLaDOS' personality makeup. Chell and GLaDOS are reunited, and partner to stop Wheatley before his incompetence destroys the complex, while GLaDOS struggles with the revelation about Caroline.

Chell and GLaDOS eventually reach the main facility again and face Wheatley who puts them through further test chambers, being driven to do so as a result of hardwired programming. In a final "surprise", Wheatley tricks Chell into a series of death traps, GLaDOS denoting that "this is the part where he kills you", but Chell deftly escapes from Wheatley's clumsiness, and makes her way to Wheatley's chamber. In their final confrontation, Chell distracts Wheatley by adding defective core modules in order to allow GLaDOS to initiate another core transfer and put herself back in control of the facility. As the facility's roof collapses, Chell shoots a portal at the moon, sucking her and Wheatley into space. GLaDOS manages to pull Chell back inside while leaving Wheatley to be stranded. Some time later, Chell wakes up, and GLaDOS explains that she learned valuable lessons about humanity from her Caroline persona. She then deletes this aspect of her personality, reverting to her standard antagonistic attitude, but finally allows Chell to leave the facility, explaining that trying to kill her has proven so difficult that it's easier to just let her go. The game ends as Chell is taken to the surface, and after a brief interlude of being serenaded by a choir of turret guns, exits from an unadorned shed into a wheat field; the charred and battered Weighted Companion Cube, supposedly incinerated from the events in Portal, is spit out from the door before it slams shut. In the epilogue, Wheatley floats aimlessly through space and expresses regrets about betraying Chell.

Co-op campaign

Two new characters are introduced in the two-player cooperative mode, which has its own unique plot and setting. These two characters are Atlas and P-body, a modified personality core and turret gun, respectively; both units are bipedal and equipped with their own portal guns. Though once part of the networked facility, they have become separate entities and are treated to similar abuse by GLaDOS through a series of complicated test chambers through her "Cooperative Testing Initiative". The robots make "expressive noises" in place of distinguishable dialogue, first stated by Valve's Doug Lombardi. The robots' mannerisms were designed to be a double act similar to Laurel and Hardy. GLaDOS appears to be troubled by the robots working together, and will attempt to aggravate their relationship through verbal trickery such as praising one robot over the other. Though the co-op story takes place chronologically after the single player campaign and has some ties into it, Wolpaw claimed that players do not "necessarily need to play them in that order". The robots are briefly introduced in the single player campaign, having been found by Wheatley while Chell and GLaDOS were climbing from the bowels of the facility, and, in the conclusion, mentioned by GLaDOS as a non-human replacement for her testing subjects.

In the co-op campaign, Atlas and P-body are shown to five sets of test chambers by GLaDOS. In the first four of these, GLaDOS prepares the robots to "venture outside" of the test systems of Aperture Laboratories to recover a data disk, after which she destroys them, restoring their memories to new bodies, as it is the only way she can recover them from "outside". Collectively, the data points to the location of "the Vault", where GLaDOS claims humans can be found. At the conclusion of the fifth test chamber, the robots discover and gain entry into the Vault, a giant structure where thousands of human bodies in cryogenic suspension are found. GLaDOS gleefully congratulates the robots, seeing the humans as new test subjects for her to process.

Development

Valve's Doug Lombardi commented that Portal was originally included as an add-on product to The Orange Box as, to Valve, it was a piece of trial software and had considered The Orange Box as a safety net if it failed; Lombardi stated, "There was no way we could have planned for the success of Portal." After Portal received high praise and proved its worth, Valve determined that its sequel should be its own product, committing more resources than it did for the first game. Compared to the previous Portal team that consisted of about 8 people, Portal 2 had a dedicated 40-person staff working on its development. Valve President Gabe Newell has stated that they know what players are looking for in the full sequel, and expect that Portal 2 will be "the best game we've ever done." Project manager Erik Johnson commented that the first Portal caught people by surprise and "made them think about games in a different way". Johnson believed their goal with Portal 2 was to find a way to "re-surprise" players, and considered that a "pretty terrifying" prospect. Original Portal designer Kim Swift, however, has left Valve to join Airtight Games.

After Portal 2's release, Newell stated that he believed that the game "will probably be Valve's last game with an isolated single-player experience", as reported by Geoff Keighley in his report "The Final Hours of Portal 2". Keighley later clarified that though he agrees it is a "proactive statement", the use of the word "probably" suggests that Valve is still open for change. Newell later reiterated that Valve is not "giving up on single-player at all" but looking to include more social features on top of the single player experience, akin to the cooperative mode present in Portal 2.

Design

Portal 2 introduces paint-like gels that affect the physical nature of surfaces they coat. Here, the blue Repulsion Gel, carried over the turret guns by the faint blue Excursion Funnel beam, causes the painted turrets to bounce off any other surface.

Work on Portal 2 began almost immediately after the release of Portal in The Orange Box. Initial ideas for Portal 2 considered dropping the portal aspect from the game; instead, the player would still participate in Aperture Science Laboratories testing a device centered around a new type of physics-based puzzle. For six months, Valve focused on a mechanic called "F-Stop"—the specifics yet known outside of Valve as they have considered using the mechanic for a new game. When Valve presented these ideas to others for comment, the lack of portals was criticized. Valve therefore returned to the portal mechanic and sought what other physics mechanics could be incorporated with portals into the larger game. One of these was a gel mechanic that can alter the physics of surfaces coated with that gel. Valve found that this addition gave players more control over the game world, but as a result, required the chamber designer to be more devious with their solutions to account for the various possibilities of the gel mechanics. The gel mechanic comes from Tag Team's Tag: The Power of Paint, a DigiPen student-developed game that won the 2009 Independent Games Festival Student Competition prize. Valve's vice president of marketing, Doug Lombardi, said that upon viewing the student game then, "the decision to combine their tech with Portal 2 came naturally". Wolpaw recalled that they had already considered the nature of surfaces in Portal in a binary fashion, whether or not it would allow for a portal to be created on it, and the ability to modify surface properties in the manner that Tag did was an obvious extension on that. Subsequently, Tag Team was hired by Valve, though initially their work was to "develop Tag in an interesting way", according to Wolpaw, only some time later being brought into the Portal 2 team. The Tag Team members were able to work out the interaction of the paint mechanics with portals, leading to new types of puzzle features in the game. Journalists compared this to the evolution of Narbacular Drop, another DigiPen student project, into the basis of Portal. While Tag features three paint types, only two have been shown to be included with Portal 2; the third, one that allowed the player to walk on any surface coated with the paint, was originally included, but this induced motion-sickness in playtesters and was dropped. Instead, new gel types were designed to be included in the game, according to Wolpaw, ultimately leading to the white Conversion Gel. The gels themselves are rendered using new fluid dynamics routines included in the engine to simulate their blob-like nature. Portal 2 also contains advanced rendering techniques for liquids that were developed from Left 4 Dead 2. Portal 2 combines the concepts of "flowing" surface maps to mimic the motion of water in a setting, along with "debris flow" maps and random noise to create realistic real-time rendering of water effects. Johnson stated that Valve's aim was not to make Portal 2 more difficult than its predecessor, but instead wanted to keep the same idea of a game "where you think your way through particular parts of the level, and feel really smart when you solve it".

Several of the early test chambers in Portal 2 reused the original chambers from Portal, adding deterioration and aging to provide familiarity to the player while suggesting the length of time between the two games.

Portal 2 was designed to give the player incremental steps in understanding portals and their use within the game. This approach led to two basic types of chambers. The first type, which Valve calls "checklisting", provides a relatively safe environment for the player to experiment with a fundamental aspect of a new gameplay concept. The second type of chamber is one that combines these elements in new ways to make the player think laterally, giving the player a rewarding experience for completing the chamber. Chambers were first developed through whiteboard via isometric drawings, with the developers performing a sanity check on the chamber, before being created into simple levels through the Hammer level editor. Extensive playtesting was used to make sure the solutions to each chamber were neither overtly obvious nor difficult to see, and to observe alternative solutions discovered by playtesters; based on their input, the design team would keep these alternate solutions viable within the level, or would work around and block the alternate solutions if they were too easy. Once a chamber was considered ready to proceed, the Valve artists then would add elements such as detailed texturing, dynamic lighting, and vegetation, using an advanced version of the Source engine. These versions would then be sent back for further playtesting to verify the new elements did not prevent players from finding proper solutions, with further iterations between artists and playtesters until such issues were resolved.

Several early chambers the player experiences in Portal 2 were created by reusing the Portal test chambers, and applying decay, collapse, and overgrowth on them. As an initial goal in the sequel, this was done to give players a sense of nostalgia from the first game and a feeling for how much time has passed. It also allowed the team to avoid the use of the less-resolved textures from the first game, replacing them with higher-resolution dirty and worn-out textures that the newer engine could support. Many of the mid-game puzzles take place in much larger and open areas of the old Aperture Science facilities to make the space "feel epic", according to programmer Jeep Barnett. In these levels, the developers had to ensure that players would hear the dialog lines and could not simply use portals to cross the chamber by making most of the surface unable to accept portals. In the final part of the game, where Wheatley had taken control of Aperture Science, "the level designers just had a blast" in creating the deranged chambers, according to Pinkerton. The level designers recognized that players would become mentally tired of completing a number of similar chambers in a row, and introduced "experiences" for the player every three or so chambers to give the players' mind a rest while expanding on details of the game's story.

The co-operative gameplay came about from requests from players as well from anecdotes of players working together on the same computer or console to solve the game's puzzles, likened by Wolpaw to players working together on the same computer to solve point-and-click adventure games. The co-operative campaign was also inspired by Valve's Left 4 Dead co-operative games, where players would find enjoyment after playing the game, discussing their personal experiences with the game. While the single player campaign in Portal 2 is designed to avoid frustrating the player, the co-operative levels are more focused on coordination and communication, and are recognized by Valve as being much more difficult than the single-player puzzles. Valve had avoided including timed puzzles into the single player experience in both Portal and Portal 2, but found that the inclusion of these into the co-operative mode was effective, giving players a positive feeling after being able to plan and execute difficult maneuvers. Other puzzle elements, such as the light bridges, are further inspirations from Left 4 Dead. Each puzzle chamber in the co-operative mode was assured of requiring four portals to solve as to prevent puzzles being solved by only the actions of one player; as soon as someone discovered a way to complete a puzzle with one set of portals, the level was sent back to the drawing board to correct this. Except in few cases, the chambers were designed where neither player would remain out of sight of the other in order to promote communication and cooperation. Some of the puzzle chambers were designed as asymmetric chambers, where one player would manipulate portals and controls to allow the other player to cross the room, helping to emphasize that the two characters, while working together, are also separate entities. The ability to tag surfaces with instructional icons for one's partner was soon realized as a necessary element, as it was found to be much more effective for cooperation than through simple verbal instruction.

In addition to the cooperative mode, Valve had considered a competitive mode. According to writer Erik Wolpaw, the mode resembled a variation of speedball where one team would attempt to transport a ball from one side of the playing field to the other using portals, while the other team would attempt to stop them with their own use of portals. While Wolpaw said the matches would begin with this objective in mind, they would quickly descend into chaos. Instead, they realized people enjoyed solving puzzles with portals more, and focused on the cooperative mode.

Writing

Erik Wolpaw returned to write out the game's script in addition to Chet Faliszek, main writer for the Left 4 Dead games and past Old Man Murray partner with Wolpaw, and National Lampoon veteran Jay Pinkerton. Wolpaw and Pinkerton were mainly responsible for the single player campaign's story, while Faliszek focused on the lines for GLaDOS in the cooperative campaign. Though the writers were aware they needed to create a larger story for a stand-alone title, they wanted to make the story "feel relatively intimate" and avoid adding too many new characters. The writers were also considered about simply expanding more on the same "sterility and dryness" from Portal, and sought to inject more comedy into the work. Wolpaw noted that while video game developers have tried to drive towards video games as art, no one has set out to make a comedic video; Wolpaw considered that "let's make Caddyshack, and then we can make Anna Karenina or whatever". Valve has stated that the game contains over 13,000 lines of dialog between the single player and cooperative campaign. The game's story was developed in tight coordination with the gameplay, developing the plot alongside each testing build for the game. In writing the story alongside in-game achievements, the writing team had to avoid placing too many spoilers in the achievement descriptions. In one example, the achievement for reaching Wheatley's death trap, named "The Part Where He Kills You", was left vague enough to make players believe that the "he" referred to Cave instead of Wheatley, such that no major spoilers about the true ending were guessed at before the game's release, according to Wolpaw.

In conjunction with the F-Stop mechanic, Portal 2 was initially envisioned to be a prequel for the first game, set in the 1950s before GLaDOS's takeover of the Aperture Science facility, with the player in control of Cave Johnson trapped within a computer. It later became a sequel, set hundreds of years after Portal, but originally had placed Cave Johnson as the main villain of the game, before reintroducing GLaDOS as a antagonist. The story for Portal 2 mirrors ideas from the first game; to contrast the destruction of the Aperture Science facility by the player in Portal, the new game starts with the reconstruction of the facility by GLaDOS. This helped to create the image of Aperture Science as a "living, breathing place", with GLaDOS given full control to restructure and arrange the setting as she needed it, according to Wolpaw. While they introduced new characters into the game, the focus of the story in Portal 2 remained the connection and interaction between Chell and GLaDOS, and focuses more on the fallout from Chell's destruction of GLaDOS from the first game.

Characters

See also: Development of GLaDOS

"Well done. Here come the test results: 'You are a horrible person.' That's what it says. We weren't even testing for that."

—Example dialog from GLaDOS in Portal 2

GLaDOS, the primary antagonist for Portal, returns as a major character within the sequel, with Ellen McLain returning to provide voice work for the character. Johnson compared GLaDOS to "a jealous ex-girlfriend" for the player-character Chell, noting "[Chell is] the only person she can have interaction with, but the problem is her only way of interacting with anyone is to test them". Wolpaw also compared GLaDOS to The Sopranos character of Livia Soprano, being "incredibly passive-aggressive and mildly sarcastic". The plot was designed to move GLaDOS from the space where she was angry with Chell, which Wolpaw believed "was going to get old pretty quick", to a scenario where she would need to deal with an internal struggle as part of her overall character arc. This was also found necessary in playtesting, as testers did not respond well to GLaDOS, embedded in a potato on the player's portal gun, would continue to chastise the player.

See also: Development of Chell

Valve originally had explored using other characters for the protagonist in Portal 2 before returning to the silent player-protagonist character of Chell from Portal. In early playtesting for the game, Valve had omitted Chell, believing her story to have been done with Portal, and introduced a new player-character; though playtesters were able to accept playing as a different character for the first part of the game, they became disoriented when GLaDOS did not recognize their player-character. Valve reintroduced Chell as the player-character, believing that it was not so much the specific character but the "continuation of the player's experience", and what they did to GLaDOS in Portal that was valued, according to Wolpaw. Early envisioning of Chell had placed her in a more utilitarian outfit, but the Valve artists later returned to the orange "dehumanizing" jumpsuit used in the first game, but now partially disrobed to the waist; this change alluded to more freedom of movement and the athletic ability to complete the chambers, to having Chell stand out from being just a numbered test subject, and a sense of familiarity to players of Portal. As in the first game, Chell's facial appearance is based on voice actress Alésia Glidewell.

Stephen Merchant (top) voices Wheatley, the personality sphere, while J.K. Simmons (bottom) voices Cave Johnson, the eccentric CEO of Aperture Science.

See also: Development of Wheatley

Personality spheres represent new characters within the game; Johnson contrasted them to non-player characters from Half-Life 2, as the personality spheres are "story-delivery type of character[s]" help to establish more of the game's backstory than they could do in Portal. The writing team noted that the use of the personality modules allowed them more freedom than in other games for developing these as characters; they would not require facial or body animations, and they could envision the use of more recognizable voice actors for each module. Although they initially thought of using six or so modules throughout the game, they decided to simplify the story and stuck to a single module, Wheatley. Some of these spheres were reused in the game's finale, but many were cut. One example given by Wolpaw would be a sphere influenced by Morgan Freeman's character Red in The Shawshank Redemption that would known every detail of a ten by ten room, and be fascinated by anything that existed outside of it. Wheatley is voiced by Stephen Merchant, though initial technology demonstrations had used Valve animator Richard Lord in his place; Valve eventually revealed that Stephen Merchant voices Wheatley in the shipped product. the writing team had created the lines with Merchent in mind, citing his distinguishing "vocal silhouette" and ability to ad lib in a "frantic" manner to convey information in a short period of time. They had assumed Merchent would be unavailable and contacted The IT Crowd's writer Graham Linehan to try to get Richard Ayoade, but later discovered that Merchent would be happy to work on the project. Merchant spent about sixteen hours recording lines for Valve, and was given freedom to improvise his role.

See also: Development of Cave Johnson

Another character, the voice of Aperture Science's founder and CEO, Cave Johnson, is portrayed by J.K. Simmons as announced at the 2011 PAX East exposition. Johnson was envisioned since Portal as a "industrial, Southern guy" who would contrast the "anti-septic" and "politically correct" nature of Aperture Science. Though their idea of the character underwent several changes over the development, the selection of J.K. Simmons helped to solidify the character. Pictures of Cave Johnson appear throughout Portal 2, and though Valve used a casting call to try to find someone to use as a template, they turned back to their own lead animator, Bill Fletcher, for Cave's face. Though comparisons have been made between Cave and Andrew Ryan, the wealthy industrialist that created the fictional underwater city of Rapture in BioShock, Wolpaw claims they had not considered this character in their creation of Cave. The writers found they needed another character to play off of Cave during his recordings; instead of hiring a voice actor for a few lines, they economized by reusing McLain to play Caroline, Cave's assistant. This led naturally to providing a backstory for the creation of GLaDOS, who is revealed in-game to be based on Caroline's personality. This later led the writers to develop a full story arc for GLaDOS where she would come to recall her past, learn from it to solve the dilemma and then subsequently delete it and reset herself.

In addition to these new characters, Nolan North provides voice for malfunctioning turrets. Though new characters were introduced, Wolpaw stated that they wanted to maintain the one-on-one relationship between each character with the player-character. Even when they had two characters talking to each other, they wanted more to have the player simply be a silent observer for the conversation, and made the situations more engaging while the dialog continued. Wolpaw also identified that, in the end, the three characters of GLaDOS, Wheatley, and Johnson contrasted well with each other. Wolpaw considered that the ending of the game is actually three endings, one for each of the main character: GLaDOS learning a lesson and promptly deleting it, Chell achieving escape into an unknown world possibly still controlled by the Combine, and Wheatley actually having learned a lesson and being apologetic for that; Wolpaw recounted that "Never really had a boss monster offer me a sincere apology for all the trouble that he’s caused me".

Story

Wolpaw and Faliszek also consider the Aperture Science facility as its own character within the game. Faliszek described Aperture Science as "a science company that's gone mad with science, where they put that first in front of everything else". Though parts of the history of Aperture Science were revealed within the first game and through ancillary materials associated with it, Faliszek says that the player will learn more about the company including "lot of the behind-the-scenes stuff".

The co-operative campaign contains a separate story between the two robotic characters and GLaDOS. The co-operative campaign includes additional dialog from GLaDOS; the original dialog Wolpaw wrote for GLaDOS was aimed to two women, Chell and a new character "Mel", with the assumption of "image issues", but this dialog remains in place even after the change of the co-op characters to robots. The dialog written for GLaDOS in the co-operative campaign is aimed to try to break the bond between the two robot characters. Valve considered initially to have separate lines for GLaDOS that would be given to each player individually, but found this to be a significant effort for minimal benefit. The writers also attempted adding GLaDOS lines that would make the players attempt to compete against each other, such as the awarding of meaningless points, but playtesters did not respond well to these lines. Faliszek noted that in co-operative games, it can be difficult to deliver key dialog or in-game events to the unpredictable players, who may not have been looking in the right direction at the right time; instead, using lessons learned from Left 4 Dead, Faliszek and Wolpaw kept the story and key comedic lines short but frequently repeated. The two robotic characters created for the co-operative mode were originally based on designs similar to the movie Westworld, looking more human and less robotic. They eventually redesigned the two characters as a modified personality sphere and turret gun, reflecting the character of the Aperture Science facility. This change also took into account the likely numerous deaths players would endure while trying to solve the puzzles together; with human or human-like characters, the deaths would be rather gruesome, but with robotic characters, Valve was able to provide more comical animations as the robots met their fate, such as struggling from being crushed by a lowering ceiling. The artists found the robot design alone related much of the character's background, in part due to the imagery from the previous game, as well as emphasizing the co-operative mode through the robots holding hands.

Wolpaw commented that while many story elements of Portal are revisited in the sequel, he did not want to return to some of the memes, such as "the cake is a lie", that have been retread over the past few years; Wolpaw stated, "If you thought you were sick of the memes, I was sick of it way ahead of you". However, Wolpaw stated that "we couldn't resist putting in just one" cake joke. Faliszek stated that they did not attempt to predict or write to lead to any other memes, believing that "you can't really plan for [dialog to become a meme] because if you do it probably seems weird and forced". There are separate ending sequences for both the single player and the co-operative campaign, including different surprises similar to "Still Alive".

Music

The indie rock band The National composed a new song, "Exile Vilify", for inclusion in Portal 2.

After finding that Jonathan Coulton's song "Still Alive" was a large part of Portal's success, Valve included more music in Portal 2, including further involvement from Coulton. Coulton wrote a new song for the game's ending credits, "Want You Gone", which is written from GLaDOS's viewpoint of wanting to rid herself of Chell. Another original song, "Exile Vilify", was provided by the indie rock band The National. The National had expressed interest to Bug Music, their publishing label, in doing music for Valve, which the label forwarded on to Valve in discussing other music opportunities for the game. Valve and Bug Music identified The National would fit well into Portal 2, as their "raw and emotive music evokes the same visceral reactions from its listeners that Portal does from its players" according to Bug Music's spokesperson Julia Betley. Other music in the game is procedurally generated, generated in real-time based on the player's actions; Mike Morasky, the game's lead composer, claims that at least one particular piece of music "only repeats itself every 76,911 years, 125 days, 7 hours, 56 minutes and 30.3 seconds."

PlayStation 3 support

As part of the Sony press conference at E3, it was revealed by Newell that Portal 2 will be available for the PlayStation 3 and will be the only console version to include some features of Steamworks used in the PC and Mac versions, making the game in Newell's words "the best console version". The news came as a surprise to many journalists, as previously, Newell has made negative comments about the system, calling it "a total disaster on so many levels" in reference to the difficulties in porting The Orange Box to the console. Newell jokingly referred to these comments by thanking Sony for "their gracious hospitality and not repeatedly punching me in the face", and said that he was nervous because he was introduced to Sony marketing character Kevin Butler as the "VP of sharpening things".

Portal 2 is the first game on the PlayStation 3 to support a subset of features from Steamworks, including auto-updates, downloadable content, and community support. The game supports cross-platform play between the PlayStation 3 and the Windows and Mac OS X versions; this was a sought after goal with the use of Steamworks on the PlayStation 3. On the PlayStation 3, the Steam overlay shows the player's friends on both Steam and the PlayStation Network, and achievements earned in Portal 2 are rewarded for both Steam and PlayStation Network trophies.

Because of the integration of Steamworks on the PlayStation 3, Valve is able to collect data on bugs and other problems that may arise after shipping, and can release patches regularly to fix these or normalize features across the three Steamworks platforms. Valve stated they did not plan on integrating other PlayStation 3 features, such as 3D television or PlayStation Move support. Despite some reports that Move support would be included, Valve has clarified that the game will not support Move. Valve contrasted this to the support the game has for the Razer USA Hydra Motion Controller, including additional levels designed specifically for the controller; according to Faliszek, the Razer developers spent nine months in-house with Valve to help bring in the controller compatibility with the Microsoft Windows version, while they would have needed a similar level of effort to incorporate the PlayStation Move controller. Faliszek further explained that the initial reports on the Move support were due to a translation error during an interview.

Downloadable content

Similar to Team Fortress 2, the co-op mode includes a means for users to customize their bot characters through cosmetic items such as hats or flags. These can be earned in-game, traded with other players, bought through the in-game store or given away as part of Steam sales promotions.

According to VP of marketing Doug Lombardi, Valve plans to produce downloadable content for Portal 2, with the first set of content expected to arrive in mid-2011. This content will be free for all users regardless of platform, and will include new test chambers, and a similar "challenge mode" that appeared in the first Portal where players must complete a chamber under specific time, movement, or portal restrictions or with new elements added to each room. The challenge modes will be available for both single player and co-operative modes.

Portal 2 also supports end user-made levels on the Windows, Mac OS X, and PlayStation 3 (made available by Steamworks), while Valve provides more direct support for these levels on the Xbox 360; some reporters believe they use a similar method that the developers used for Super Meat Boy to bypass the Xbox Live Marketplace for additional content. The tools to make these levels will only be available on the Windows platform due to software dependencies.

Promotion

Announcement

File:Portal-2-ARG-SSTV-Images.png

Part of the alternate reality game that led up to Portal 2's announcement was the decoding of SSTV images embedded in an update of the original game.

After Portal's release and critical success, Valve employees Doug Lombardi and Kim Swift, indicated that "more Portal" will be coming. Swift suggested the sequel may contain a multiplayer element, but only if this "from a technology standpoint is possible". Previous comments from Swift had suggested that a multiplayer Portal was "less fun than you'd think." On June 10, 2008, Kotaku reported that Valve was seeking voice actors for the character role of Aperture Science CEO Cave Johnson and suggested that the second game may be a prequel to the events in Portal. However, a later update suggested it could be a sequel, with Johnson as another AI.

The sequel was officially announced on March 5, 2010, but events within the week before this foreshadowed the announcement. On March 1, 2010, a patch was released for Portal. The patch included an additional achievement, "Transmission Received", requiring the player to manipulate the in-game radios in an appropriate manner. This revealed new sound effects that became part of an alternate reality game-style analysis by fans of the game; the effects included Morse code strings that implied the restarting of a computer system, and SSTV images from a grainy Aperture Science video. These images embedded further hints of a BBS phone number that when accessed, provided a large number of ASCII-based images relating to Portal and segments of fictional documents for Aperture Science; many of these ASCII pictures were published art assets for the game as shown in the Game Informer reveal of the title. A second patch two days later altered the game's original ending to suggest Chell's current fate, with additional digital files and resources to further the alternate reality game. These events were seen by gaming journalists to be leading to a forthcoming Portal 2 or other Half-Life game announcement. Following these events, in time with a countdown timer on the BBS, Portal 2 was officially announced. Details of this alternate reality game were embedded in additional SSTV audio-encoded images within a hidden room within Portal 2. According to these, the game only had a budget of $100 to produce and designed to attract both casual players via the finding of radios in Portal, and the more enthusiastic players through the decoding and deciphering. The BBS was based on a personal computer being run out of the kitchen of one of Valve's employees as the Valve office phone lines were too modern to support a BBS.

Gabe Newell continues the alternate reality game surrounding Portal 2's announcement during the 2010 Game Developers Conference.

The alternate-reality game continued after the game's announcement. New ASCII images continued to appear on the BBS after the official announcement. At his acceptance speech for the Pioneer Award at the 2010 Game Developers Conference, occurring the week following Portal 2's announcement, Gabe Newell ended his speech presentation with a fake blue screen of death, purporting to be from GLaDOS and hinting at further Portal 2 news at the Electronic Entertainment Expo 2010 (E3). Two weeks prior to Valve's planned presentation at E3, a cryptic e-mail received by game journalists, purportedly sent as a press release from Aperture Science, hinted that the presentation of Portal 2 was canceled but was to be replaced with "a surprise" jointly by Aperture Science and Valve; this has led to some speculation that Half-Life 2: Episode Three may be announced alongside further reveal of Portal 2. In the week prior to E3, Valve reiterated that the "surprise" at E3 would still be about Portal 2, but noted that the game's release has slipped to sometime in 2011, humorously referring to the preservation of "the fabric of Valve Time". The surprise at E3 was revealed to be the development of the PlayStation 3 version of Portal 2 with partial support for Steamworks on the console, a dramatic reverse of Valve's previous statements on the console.

Portal 2: Lab Rat

An abandoned area in Portal 2, showing the effect of flora overgrowth and deterioration on the Aperture Science facilities. The art on the wall, created by the "Rat Man" character, depict the events of the first game, and also tie in with the "Lab Rat" comic.

To help develop the history of Aperture Science and the span of time between Portal and Portal 2, Valve expanded upon the unseen character of the "Rat Man" in both Portal 2 and through a digital comic, "Portal 2: Lab Rat". Within the game, the Rat Man's triptych-like artwork is seen by the player at the start of the game, used to recap the events from Portal, and in playing through some test chambers. Valve's in-house artist Andrea Wicklund created the graffiti-like style for the game. The two-part comic was developed in-house by Valve with the aid of Michael Avon Oeming, who had previously helped Valve with comics for Team Fortress 2 and Left 4 Dead. The comic, made available online about two weeks before Portal 2's release, includes Wicklund's art contrasted against Oeming's own style and layout, along with an overall story written by Ted Kosmatka. The artists worked with the game's writers, Laidlaw, Faliszek, Wolpaw, Pinkerton and team leader Josh Weir to tie the comic's story, taking place between the two games, to the plot of Portal 2.

Within the comic, the Rat Man, a scientist at Aperture, escaped from the neurotoxin released by GLaDOS that wiped out the rest of the Aperture staff, and slowly became insane. However, he sees that Chell is unique for her tenacity among the thousands of test subjects stored by Aperture, and seeks to protect her, moving her to the top of the list subject queue to allow her to escape. He wrote messages on walls to guide and warn Chell during the events of the first game; having witnessed GLaDOS's defeat at the end of the first game, the Rat Man's drawings created in the months after the events summarize the first game during Portal 2's introduction. Rat Man, though able to escape after GLaDOS's destruction, returns to the facility following the robot that drags the unconscious Chell back inside. As a final act, he ensures that Chell is kept in indefinite cryostorage, before he himself enters a cryogenic unit after being severely wounded by turrets.

Marketing and release

Portal 2, on its March 2010 announcement, was originally set for release late 2010. In August 2010, Valve announced that the game's release had slipped to February 2011, with a planned Steam release date of February 9. Valve announced a further delay of the game in November 2010, setting the week of April 18, 2011, for release worldwide through retail and online channels. On February 18, 2011, Newell confirmed that Valve had completed the development work on Portal 2, and that they were "waiting for final approvals and to get the discs manufactured" in anticipation of this release date.

Portal 2 is the first Valve product simultaneously released for Windows and Mac OS X computers through the Steam platform. Retail copies of the game for Windows, Mac OS X, Xbox 360, and Playstation 3 are distributed by Electronic Arts. As part of the PlayStation 3 release, those who purchased the PlayStation 3 version of Portal 2 are able to unlock the game on the Steam platform for Windows and Mac OS X for free by linking their PlayStation Network and Steam accounts, and using a redeemable code within the PlayStation 3 packaging. Faliszek explained that despite the additional support for the PlayStation 3 version, "the core game, whether you buy it on PS3 or 360 is the same, you're not going to lose out anything on that".

Portal 2 will be bundled as part of the release package for the Razer USA Hydra motion controller for personal computers in mid 2011. In conjunction with Valve, Razer USA developed additional Portal 2 levels to be used specifically with the motion controller.

Valve created their own series of television commercials for promoting Portal 2. According to Lombardi, though they had worked with advertising agencies in the past to create advertisements, Valve found the agencies to provide little ingenuity towards their games; Lombardi's frustrations included "Copycat treatments. Cliché treatments. Treatments that reveal the agency wasn't listening in the initial meeting." By creating the ads themselves, Valve was able to tailor the content based on feedback until they were satisfied with the results. The ads took eight weeks to complete. Valve also developed additional online promotional videos, featuring J.K. Simmons narrating as Cave Johnson to promote new elements of Portal 2's gameplay. These videos were part of a larger effort described by Newell as a "documentary-style investment opportunity" for Portal 2. An earlier video release on Valentine's Day, February 14, 2011, promoting the co-operative aspect of Portal 2 as an ideal Valentine's gift, has, according to Lombardi, "lit up our preorders, our buzz, all the metrics that are used and collected by publishers and retailers", and considered the videos to have "dwarfed the demos and interviews we did".

At the PAX East exposition in March 2011, Wolpaw stated they would provide material before the game's release to tie the timeline between Portal and Portal 2 together. The forementioned "Lab Rat" comic, produced by Valve, providing a tie-in story between Portal and Portal 2, was released about two weeks before Portal 2's availability. Valve also offered new Portal 2-themed merchandise on their own store, such as t-shirts, including one that parodies the Three Wolf Moon shirt, posters, and drink glasses.

Main article: Potato Sack

Portal 2's release was preluded by another alternate reality game called the Potato Sack across thirteen independently-developed games. Envisioned by Newell around December 2010, the developers were brought to Valve to discuss and plan the "Cross Game Design Event", to culminate with the early release of Portal 2 on Steam. The developers had been given access to Valve's art and audio assets to incorporate Potral-themed content into their games. The game was launched on April 1, 2011 with a Steam bundle sale of these titles. Players, coordinating efforts through web sites and chat rooms, worked to solve the multi-tiered puzzle, which some journalists believed pointed to the release of Portal 2 on April 15, 2011 instead of the target release date of April 19, 2011. Eventually on April 15, the players discovered "GLaDOS@Home", a distributed computing spoof that encouraged participants to play the various games to unlock Portal 2 earlier. As a result of coordinate efforts, the game was unlocked about ten hours earlier.

The game includes bonus content based on the 2011 film Super 8. The content is a small level constructed within the Source engine, serving as an interactive trailer inspired by the film.

Reception

Reception

Aggregate scores

Aggregator	Score
GameRankings	95.2% (PC) 93.8% (PS3) 94.6% (360)
Metacritic	95/100 (PC & PS3) 94/100 (360)

Review scores

Publication	Score
1Up.com	A+
Edge	9/10
Eurogamer	10/10
G4	5/5
Game Informer	9.5/10
GameSpot	90/100
IGN	9.5/10
PC Gamer (US)	94/100

Portal 2 was a strong favorite of gaming journalists from closed-door previews at the 2010 E3 convention. The Game Critics Awards, selected by a large number of journalists and critics, awarded Portal 2 the title of Best PC Game and Best Action/Adventure Game, and nominated the game for Best of Show and Best Console Game. IGN named Portal 2 as its Best of E3 for PC, Xbox 360, and PlayStation 3 systems as well as Best Puzzle Game, further nominating the game as Best Overall Game. Gamespy named Portal 2 the Best Overall Game and Best Puzzle Game of E3. Portal 2 has also won the Spike VGA award for "Most Anticipated Game for 2011".

On release, Portal 2 received universal praise from reviewers, resulting in a accumulative average score of 95 out of 100 according to review aggregator Metacritic; several reviewers identified Portal 2 as an early contender for "Game of the Year", while others identified the title as one of the best games of all time. Prior to launch, several critics expressed concern that Valve might be unable to take the shorter, experimental, Portal from The Orange Box and make it into a full retail game, but upon release the game was widely considered to be as good or better than the original. Eurogamer's Oli Welsh stated "Portal is perfect. Portal 2 is not. It's something better than that", with the game able to avoid the normal pitfalls that developers introduce in sequels. Gus Mastrapa of the A.V. Club commented that, with Portal 2, Valve alleviated any doubts that "Portal could be expanded into a big, narrative experience with all the bells and whistles of a mainstream gaming hit". IGN's Charles Onyett considered that the sequel "makes the original look like the prototype it was" by expanding the game in both gameplay and story. Similarly, Wired's Chris Kohler felt that Portal 2 avoided the pitfalls of most sequels and instead was "the perfect marriage of sharp young designers' fresh ideas and big-studio polish". Ryan Kuo from the Wall Street Journal contrasted the sequel to its original game as "If Portal was a song, then Portal 2 is the song, its liner notes, critical annotations, and remastered anniversary edition". Brett Molina of USA Today claimed that Portal 2 passes the hype of being the sequel to Portal "with flying colors" and considered the title "easily the year's most imaginative and engrossing video game".

Reviewers praised the writing and voice acting in the game. CNN's Larry Frum identified that "the writing and dialogue remain one of the cornerstones to this series", with dialog that remains "dark and dangerous" likes its predecessor. Evan Narcisse of Time considered that Portal 2's writing "evinces a certain weariness and wariness" suitable for the game's plot of Chell versus GLaDOS in contrast with the predecessor's "chilly and academic" dialog. Mike Nelson of 1UP.com considered that the game's "tight writing and quick dialog" serves well as "Valve dangling a carrot" in front of the player to continue forward in the game to explore its story while solving the puzzles along the way. Entertainment Weekly's Dan Stapleton of PC Gamer was able to predict many of the plot twists within Portal 2's story but "still looked forward to witnessing exactly how the characters would react", praising the development of the characters as "their charm makes what would otherwise be an empty and lifeless world feel boisterous and alive". Garrett Martin of the Boston Herald concluded his review of the game as "Portal 2 is as good as entertainment gets." In contrast, Peter Bright of Ars Technica commented that compared to the loneliness and despair he felt while playing the first game, the additional characters, specifically Wheatley and GLaDOS, lost some of this feeling and "the inane babble served only to disrupt the mood".

John Young of Entertainment Weekly identified Valve's writing as having a "delectably British sensibility to the jokes" and praised Merchant as Wheatley, claiming the personality sphere is "the most delightful artificial-intelligence program one could hope to meet". Oynett believed that Merchant's "obvious enthusiasm for the role benefits the game", and that the "consistently clever writing perfectly complements the onscreen action". Morgan Webb of G4 TV claims as "GLaDOS is just as creepy and funny" as she was in Portal, "Wheatley’s emotional banter is the perfect foil to GLaDOS’s deadpan". Edge also considered Wheatley as an "unforgettable presence" within Portal 2 in part to Valve's animation of the character and story machinations. Edge also praised the selection of Simmons for the character of Cave Johnson, the "surprise star turn" of the game, with lines that are "perfectly pitched, and funny to the bone". Game Informer's Adam Biessener considered Johnson to be an even better character than GLaDOS, a tribute to "pitch-perfect delivery" with "brilliant comedic timing" that Valve included in the game. Chad Sapieha of the Globe and Mail called the selection of Simmons "brilliant" to create the "perfectly pompous and maniacal personality" of Cave Johnson. Oynett noted that the game's second act, in which the player explores the past of Aperture Science, is somewhat slower-paced than other parts of the story, but still remained "far more creative and confidently original" than most other video games. Kuo also commented on this act, that Simmons was "more grating" than the other characters in the game, and for himself, "the whys and wherefores of Aperture’s past are less interesting, to me, than the current state of affairs".

Portal 2's additional gameplay elements, like light bridges, lasers, and the gels, were praised as appropriate additions to the game. Narcaisse had stated that he feared the addition of the new gameplay elements would "dilute the purity of the experience", but instead of pleased with the results, as "everything's still executed with Valve's high level of charm and panache". Tom Hoggins of The Telegraph praised the manner which with these elements were introduced through a "brilliant learning curve of direction, rather than instruction", and considered it a "design ethos that is supremely generous, but dealt with marvellous [sic] economy". Stapleton was not as pleased with the gel additions as with the other new mechanics, calling it "difficult to control" and that they have "only a couple of uses at most". The cooperative puzzle solving aspect was highlighted as a valuable addition of the game. Biessener stated that he was not "sure about co-op puzzle-solving beforehand, but Portal 2 made [him] a rabid believer". Welsh called the cooperative mode "one of the most satisfying and genuinely collaborative gaming experiences you can have with a friend". Onyett praised Valve for using the lessons they learned from Left 4 Dead to build the cooperative mode that requires "a game design that doesn't simply encourage but requires you to work together". Edge magazine commented that Valve had balanced both the puzzle solving alongside physical comedy in the cooperative mode, stating "When you get it right, there’s a sense of a shared achievement; when you get it wrong, it can be laugh-out-loud funny." Webb appreciated that the puzzles in the cooperative mode require more precision in timing compared to the single player campaign, giving the two "a subtly different feel". Several reviewers praised the non-verbal cues that players could initiate to work with their partners.

In general, the reviewers were pleased with the level of difficulty of the puzzles throughout the game, appearing visually complicated at first but with uncomplicated solutions. Kohler considered that the game "never require excessively complicated solutions", and that much of the puzzle solving is "filled with moments that will have you slapping your forehead". Gamespot's Chris Watters stated that Portal 2 "does a great job of introducing you to new tools and then challenging you to use them in clever ways", and that the game contains "some very tricky situations that you must puzzle your way out of, and figuring them out is always immensely satisfying". Hoggins believed that, in the process of finding the solution, "simply mucking around is enjoyable in and of itself", and that "every failed experiment is just another step towards revealing a puzzle's secrets". Will Freeman of The Observer stated that Portal 2 helps the player to think in new ways, and considered that "to experience a game manipulating your thinking processes as you play is a unique and extraordinary pleasure". Kirk Hamilton of Paste compared Portal 2's puzzles to a chain of dominoes; while the players in either the single player or cooperative campaigns may be initially confused by numerous elements within a chamber, the game guides the players to find the right sequence of events necessary to complete the chambers, themselves acting as dominoes in the chain. Sapieha summarized his review by stating "Portal 2's genius is that it makes the player feel like a genius." Bright felt that Portal 2 was easier than its predecessor, in part that he felt much of the game was effectively tutorials for the new gameplay additions, requiring "careful use of the tools provided", leaving him with the impression that "the game was on rails".

Portal 2 was also praised for detail in design, sound, and music by reviewers. Nelson credited the "sheer amount of detail" put into the game's world, and felt it was "very real and natural with brief moments where you're simply sucked into this world". Onyett was impressed with the amount of visual details and capabilities Valve achieved from their Source, and that the added details and animations of the levels "consistently serving not only to entertain the eye but to expand our understanding of the game's characters". Hoggins believed that the game's world reacted to the player "in a startlingly organic way", and praised Valve's design as "an achievement of world-building that compares favourably with BioShock's underwater city of Rapture". Stapleton stated the "everything is impressively modeled and textured", and appreciated the more dynamic visual look, as the "scripted activity animates what would otherwise be still and samey-looking rooms due to Portal's lack of foes other than stationary turrets". Some reviewers did note that the second act of the game, taking place in the less-structured portion of the old Aperture facilities, while filled with impressive vistas, may be confusing to some players. Young believed in this section the game "cranks up the difficulty level at a speed that may dishearten casual gamers", and recounted several difficulties from having "absolutely no idea where [he] was suppose to head next". Mastrapa, though praising the areas as a break from the testing chambers, felt these cavernous areas were "downright extravagant when all it takes is one portal jump to cross their gaping spans". Kohler further considered that while the player would explore the abandoned areas of Aperture, there is very little to do in these areas and called them "a lot of sterile, duplicated, non-interactive environments". Watters noted that the loading time between the game's levels, in contrast to earlier Valve games, are "long enough to make you take notice and wish they were shorter". Watters also commented on the lack of challenge chambers or other advanced features packaged with the shipped product that were present in the original, though that Portal 2 is "not light on content" without these. Welsh noted that the attempt to recapture the spirit of the song "Still Alive" in the end credits of Portal 2 "was a mistake".

Journalists noted that many of the user reviews for Portal 2 on Metacritic evoked negative opinion of the game. These users cited complaints about the game being too short (with some saying it is only four hours long), the existence of paid downloadable content at launch for some versions, and supposed evidence that the game on Microsoft Windows and Mac OS X were ports of the console version. Journalists have defended Valve in these claims, countering that the game's length depends on the amount of immersion the player puts into the game, that the downloadable content is only cosmetic additions for the co-op mode, and that the quality of the graphics on the Windows and Mac version do not suggest a simple console port. Some journalists also identify that the minimal impact of the Potato Sack alternative reality game on the early release of Portal 2 may be influencing the user scores.

Sales

Portal 2 was the most-sold game across all platforms in the United Kingdom during the week of its release, with the Xbox 360 and PlayStation 3 versions taking the first and fourth spots, respectively, for individual console game sales. This is the first time that a Valve game had placed in the first spot on these charts. It remained at the top of these charts during the second week of sales. In the United States, based on sales data from Amazon.com and other vendors, Portal 2 trailed after Mortal Kombat in sales for the week of its release. Michael Pachter of Wedbush Securities estimated that over 1 million units of the console versions Portal 2 were sold in the United States during April 2011. The influence of the PlayStation Network outage which occurred a few days before Portal 2 on the game's sales for the PlayStation 3 is yet unknown.

External links

• Portal 2 Official Web Site
• Portal 2 at IMDb