I thought Robin Williams' character was quite original and he gave a great performance as did Damon but aside from that and the great ending, most of the film is only solid and doesn't reach the level of greatness I had hoped. EDIT: Rewatched it. Really good film.
A awesome film and great screenplay by Affleck and Damon. Deserving of all of its accolades. The monologues are worth memorizing. Affleck as an actor has never been better and Williams likewise turns in a sensitive and moderated performance.
One of the best illustrations of how a strong supporting actor can completely lift a whole performance. Robin Williams' delivery is masterful as he digs deep into the main character's motivations and anxiety while coming to terms with his own flaws.