One of the things that is essential to the mystery of the Beatles is that each of the members was an integral part of the whole. Ringo's drumming is really enjoyable and some of it is just mindbendingly good (Rain, Day in the Life, Come Together). On top of that his personality was great, he was the star actor in both Hard Day's Night and Help!, the songs he sang conveyed his character.
I couldn't imagine the Beatles without Ringo, he provided the Beatles with some true Star(r) quality.