Drama is easy, comedy is hard. Very hard. A moving production of Shakespeare or Beckett are a walk in the park compared to making large groups of people howl with laughter. It's one of the reasons I've always found it hard to agree with the Oscars when riotous comedies aren't nominated.
I remember hearing a story about Robin Williams years ago. That he'd once gone on stage and done two hours of stand-up comedy for the early show that had the audience in stitches. Then, for the second show less than an hour later he did another two hours of amazingly funny stuff, and NEVER DID THE SAME JOKE. That takes funny. Real funny.
Comedy is rare talent. Few have it. Robin Williams was one of them. His performances are right there at the top of the pantheon of comedic excellence. Good Morning Vietnam was falling down funny. And I could watch him be funny in almost anything, even films I really had no intention of watching. I didn't think I would like The Birdcage, but because of Williams I watched it and was blown away. I really didn't plan to watch Hook, or Jumanji or Mrs. Doubtfire. Saw them all. His voice over work is legendary. He practically made the move Robots work. I saw Aladdin specifically for his performance as the Genie. I'm such a fan of his comedy I even thought he was good in Popeye.
The term "National Treasure" was once applied, and I actually got angry when someone questioned it.
The world today is a little less funny. No, that's not accurate, its a lot less funny, than it was yesterday. He was just that damned good.