Unlike previous Das Racist efforts, Kool A.D. recorded 51 in Oakland, California, which resulted in a more confident sound according to many critics. A.D. recruited many Bay Area producers and rappers to assist him with the creation of the mixtape, though fellow New York-based Das Racist member Heems appears on one track.
A variety of references are made throughout the lyrics of 51. Kool A.D. disparagingly references the feud between Drake and Common by commenting, "Who cares?" on the track "La Pinata." Other references in the mixtape include boxer Manny Pacquiao, artist Damien Hirst, musician Al Green, and Lady Gaga's song "Poker Face." The tracks "Oooh" and "No" sample Marvin Gaye.
51 received mostly positive reviews from critics. Many compared the album positively to Kool A.D.'s less well-received previous effort, The Palm Wine Drinkard. Pitchfork applauded the fact that "Kool A.D. is actually rapping for the most part on this one rather than further pursuing the robo-tripping path of Palm Wine Drinkard," noting that 51 is "the most consistently listenable thing out of the Greedhead camp since Sit Down, Man probably because it's the most effortlessly fun since Shut Up, Dude." In a positive review, Prefix Magazine described the mixtape as "a damn fine mixtape—album, release, whatever. It’s a trip down into Kool A.D.’s psyche, a demonstrable showing that while Das Racist might be based in New York, one of their members is spiritually Bay."Rolling Stone's Matthew Trammell, in a mixed review, wrote that "the project veers off course when A.D. taps Bay Area-beatmaker Young L, and derails entirely (and possibly intentionally) when the rapper steps behind the boards for songs like the grinding, non-sensical 'Power/Refinement Knowledge,'" though Trammell noted that the mixtape as a whole "suggest[s] that Kool A.D should record in the Bay Area more often."