Another thing I find interesting about Buster Keaton is that he was incredibly tiny, and he used this to his advantage. There are a lot of scenes of him being thrown around by escalators, larger people, etc. He could do some really amazing stuff with his body. Like Jackie Chan, he sometimes made me gasp and rewind, simply awed by his flexibility and coordination.
Oh, one other thing. When he was young, he had this very elegant, delicate, refined face. I'd never really noticed that before, but it interacts really interestingly with his humor. He just doesn't look like a comedian. And he usually kept a very straight face throughout his most outrageous slapstick.
Side note: I think the modern-day actor William Fichtner looks a lot like him.
Now I really want to rent "Benny and Joon" again. Johnny Depp -- amazingly enough -- does a charming Buster Keaton impression.