These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Base Breaker: "Revolution 9". For some, it's brillant and revolutionary; for others, it's a horrid and irritating mess.
Others split the difference, recognizing that it's brilliant and revolutionary but not actually liking it
As with most long double albums, there's the constant debate over if it would've been better as a single album, and if so which songs are filler and should be cut (it doesn't help that this is probably the album where the differences between John and Paul's writing stands out the most)
"Glass Onion" was intended as sarcastic attack on all those Beatle fans who sought for hidden messages and meanings in their songs.
Sadly, American serial killer Charles Manson still managed to interpret the lyrics of the songs "Piggies", "Revolution 1", "Revolution 9", "I Will", "Honey Pie", "Blackbird" and "Helter Skelter" as a message to start murdering other people. For his Cloud Cuckoo Lander interpretations, see this link.
The album in general has an overall harsher, unsettling quality to it. Instruments and vocals have weird textures, songs are played roughly (sometimes with proto-heavy metal distortion) and end in minor keys, songs end (or begin) in disjointed ways, Last Note Nightmares abound. Many of the songs lyrically deal with death, violence and mortality in a way Beatles records hadn't before. Even the more lighthearted songs don't help matters. The Reality Subtext of the band falling apart is audible. It's the band's darkest album.
There's also the fact the insane cult leader, Charles Manson, would twist the meanings of the songs into a megalomaniacal scheme to cause a race war through mass murder.
One-Scene Wonder: Eric Clapton came to the studio at his friend George's request to play on "While My Guitar Gently Weeps". He delivered probably the best and certainly the most skillful guitar solo to ever appear on a Beatles record.
What Do You Mean, It Wasn't Made on Drugs?: Partially subverted with the making of "Ob-La-Di, Ob-La-Da" which John Lennon, high on pot, growled he didn't like the song's preliminary slow tempo and instead went to a piano and bashed out the introduction in a louder and faster tempo. As it turns out, the rest of the band agreed that sounded better and they recorded the song with that tempo in mind.