Inspired by 1950s R&B and rock and roll numbers, the song's lyrics sing of an unrequited love, but rather than a lament are instead performed in a hysterical, "celebratory frenzy"[1] of self assuredness.

The first song by the band to incorporate a Vox Continental electric organ, John Lennon plays the instrument in the style of Jerry Lee Lewis, doing glissandos with his elbow.

[2] In November 1963, Paul McCartney moved into the family home of his girlfriend, Jane Asher, located at 57 Wimpole Street in central London.

[4] Written in the style of Little Richard, the song began as an attempt to replace "Twist and Shout" and "Long Tall Sally" as the closing number of the Beatles' concert tour set list.

[6] In his authorised biography, Many Years From Now, McCartney remembers "I'm Down" as entirely his composition, but raises the possibility that Lennon added a few lyrics or made minor suggestions in the writing process.

[1] With neither bass nor drums to clarify the key or downbeat, Pollack writes that "no matter how many times you've heard the song", McCartney's opening vocal is "an effect which retains the power to startle".

[9] Everett writes the concluding coda serves the purpose of "[raising] the rock-and-roll spirit to a higher level of excitement than does the song proper".

[1] Pollack writes the song's style originates in a 1950s R&B cliché, being "a semi-improvisatory rave-up" where the lyrics are unimportant compared to the tone in which they are sung.

[9] Riley describes the song as an instance of "dancing on your problems", as heard in rock and roll oldies like "That's All Right" and "Blue Suede Shoes".

[13] The song's basic track features McCartney singing and playing bass, George Harrison on electric guitar and Ringo Starr on drums.

[31] "I'm Down" remained relatively elusive among Beatles songs after its initial release, with critics and fans criticising Apple Records manager Allen Klein for omitting it from the 1973 compilation album 1962–1966.

[33] While authors Nicholas Schaffner and Robert Rodriguez are each generally critical of the compilation, they count the inclusion of "I'm Down" as one of the album's redeeming features.

[37] Parlophone used Martin's 1976 stereo remix when they included the song on the compilation album Past Masters, Volume One, released on CD in March 1988.

[40] Writing for AllMusic, Stephen Thomas Erlewine calls the song "peerless" and that it demonstrated the Beatles' ability to "rock really, really hard".

[42] Scholar Michael Frontani similarly compares McCartney's vocal to "Long Tall Sally", while also mentioning the "rock and roll shout" of his 1971 solo B-side "Oh Woman, Oh Why".

[54] Due to the overwhelming sound of audience screaming, technical issues with the live recording and musical mistakes on the part of the Beatles,[55] the band re-recorded and overdubbed sections of the film's soundtrack on 5 January 1966 at CTS Studios, London.

[51] Riley suggests that Lennon's unhinged keyboard playing on "I'm Down" reflected the absurdity of the Beatles' live shows, and that "[t]he band's hysteria on this song [mirrored] their fans' deafening adulation".

[63] Its inclusion on the album was blocked by the copyright owner, musician Michael Jackson, because he disapproved of several of the cover's altered lyrics, including: "I keep a loaded pistol inside my pants / Find a def girl and do the new dance."

Dave Reynolds' review of the album in Metal Forces magazine calls the cover "superb",[65] and John Franck of AllMusic describes it as "well executed".