I was very saddened by that news, but not surprised; my peers have been dropping like flies lately and the loss of another is not much of a shock anymore (just another feature of being a sexagenarian).
According to my count, Robin Williams appeared in four films that included transgender bits: Mrs. Doubtfire, The Birdcage, The World According to Garp and To Wong Foo Thanks for Everything, Julie Newmar, but in my opinion, his best film performance was in Good Will Hunting.
My favorite Robin Williams moments were when he riffed with Whoopi Goldberg and Billy Crystal in Comic Relief. They were a great team. Whoopee and Billy must be taking the loss of their teammate very hard.
I will miss him a lot, too.