i think it's reasonable to say that the best robin williams movies were generally ones where he wasn't in a lead role, like 'deconstructing harry' and branagh's hamlet and whatnot. the gilliam movies are respectable enough too although i'm not a big gilliam fan personally. i mostly just like robin williams for all the iconic roles he played in family movies over the years, i think that's what a lot of people in my generation will remember him for. older generations will remember him for his stand-up i guess, which was surely his most skillful work as an entertainer, if not really my cup of tea.
dude also played one hell of a creepy bad guy. i think part of his appeal (and i don't mean this in an insulting way, i liked him for it) was that his aura occupied uneasy spaces between friendly uncle and that guy down the road with the weird glasses who spends a bit too much time hanging around outside the school. he was a man of paradoxes and his comedy was the same; quite a lot of sadness and rage buried in that mania. in that respect his end, while tragic, isn't particularly surprising to me. always got the feeling he's one of those people who was inspired to be a comedian because the world is so damn sad.