More mature and musically complex than the fairly conventional albums that came before, Rubber Soul was the band's most serious project to date.
Number 3 on Rolling Stone's list of greatest albums, Revolver was by far the band's most ambitious studio project to date. One song, "Tomorrow Never Knows," employed every techno-trick in the book from mechanically-filtered voices to a backwards guitar track.
Rolling Stone called Sgt. Pepper's the greatest album of all time (and the Beatles' best)—not just for its music but also it conceptual basis, cover art, and studio technology.
Another Rolling Stone top ten album, this 1968 release contains some great music. But the tensions within the band were starting to surface and, as a result, the conceptual coherence of Sgt. Pepper is a thing of the past.