He had been sick with cancer for quite some time, hadn't he? I seem to recall seeing him on Oprah a few years back, and he had pretty much lost his jaw, and was unable to speak or anything... so yeah, I guess it was only a matter of time.
But yeah, he was a very well-known critic, he and Siskel (and later Roeper) both. I learned recently that in the 70s, Ebert actually co-wrote a couple of screenplays for, of all things, porno movies... I think it was with that guy they mentioned in an episode of SEINFELD where Monk's suddenly only hired busty waitresses.