Lots of experimentation with a variety of musical styles and creative instrumentation. Brian Jones in particular was a key player in moving the music forward.

The best tracks are 2000 Light Years From Home, Citadel, 2000 Man, and She's A Rainbow. The rest are mostly forgettable or (In the instance of "Sing this Togerher and See What Happens) annoying. Ditching that one and including "We Love You" and "Dandelion" would have yielded a far better product. I agree that TSMR was inspired by Sgt Pepper, although it would have been near-impossible to best that one. Going back to "Between The Buttons", I see that one as the Stones' equivalent of "Revolver" for the era encompassing mid-to-late 1966. Both bands were able to knock it out of the park IMHO.

... Satanic followed.

He knew that each member of the group had loyal fans, and as a smart business move, mandated that each of them be given a share of the spotlight. John and Paul would have been more than content to write and sing every song on every album. They were somewhat dismissive of George, but Martin was far more supportive, and in time George developed into a fine songwriter. On "Revolver", "Yellow Submarine" doesn't really fit in with the other well-crafted songs, standing out more as a trite novelty song. But Ringo's obligatory spotlight was the albums biggest hit. Martin's semi-democratic approach in deference to the group's fan base certainly boosted record sales, even though it put less emphasis on actual artistic merit.

They needed a top-notch drummer who could keep time and serve the song, and Ringo did precisely that. I'm not offended per se by Ringo's singing, but he was by far the weakest voice in the group. It's not remotely "Beatlesque" sounding as are the other three. His personal charisma and unique and readily identifiable "bad" voice got him by.

... joined. Just one of the best drummers ever, he didn't need a huge kit, he had his licks polished to speak for him.