"I Wanna Get Better" incorporates cut-up piano notes and samples into its arrangement; Antonoff's vocals range from baritone to "shout-along anthemic."
Antonoff considers the song his "mission statement" because it goes through every bad thing that has happened to him. Antonoff has stated that "the message is heavy, it’s not dumbed down" with the verses being literal and the inspiration coming from a place of sorrow following the events of 9/11, his sister's death in 2002, and his cousin's death during the Iraq War in 2003. In regards to the line "lost control when I panicked at the acid test", Antonoff has stated that he "had a horrible experience" with acid and it changed his life.
The official music video for "I Wanna Get Better" premiered on March 27, 2014, and was directed by actress and filmmaker Lena Dunham, frontman Jack Antonoff's then girlfriend. The video depicts a day in the life of a therapist (Antonoff) who, after getting dumped by his girlfriend (Kimiko Glenn), proceeds to his office and meets a variety of clients, all of whom are depicted describing their own personal problems and lip-synching to the song's lyrics. Comedian Retta and actor Mike Doyle play a couple who are suffering from marital problems, actor Rizwan Manji plays a highly-strung patient who gets distracted by "Bring Your Daughter To Work" Day, and actress Mary Kay Place plays a patient who "creates drama". Antonoff described working with Dunham as "fun", adding: "I didn't have to do anything. I felt, obviously, completely supported. It was nice to be in a position where you can’t fuck up."
"I Wanna Get Better" received critical acclaim, with some reviewers labeling it as one of the best songs of 2014. Michael Tedder of Spin lauded the song, writing that it is "an example of an artist so succinctly summing up their entire raison d’etre in one song that the accompanying album becomes superfluous". Tim Sendra of AllMusic called "I Wanna Get Better" a "flat-out excellent pop song", while Josh Terry of Consequence of Sound felt it was one of the album's best tracks due to its "abounding optimism, complete with a monster, scream-it-at-the-top-of-your-lungs chorus". A staff member for Sputnikmusic described the track as "upbeat, anthemic, sweeping, and memorable". Both Jon Dolan of Rolling Stone and Mat Smith of Clash named "I Wanna Get Better" the highlight track from the album. A more mixed opinion came from Mack Hayden of Under the Radar; he praised "I Wanna Get Better" and fellow Strange Desire track "Rollercoaster" as "great pop rock singles", but commented that "if you can listen to them more than three times without looking for something better, you're a more generous listener than me".