Actually, many American celebrities have died where I seen the news and said just "ok"...
Robin Williams was someone who cared more for others than he cared for himself, he wasn't in it for the fame or the money, his passion knew no limits, his films made me feel good, feel sad, feel excited, while his comedy made me laugh so much !
He is one of the few "celebrities" on Earth that has actually made me feel as if a member of my own family has passed on... I didn't even see him as a celebrity, I seen him as just another nice person who made our lives that little bit more fun.