This is the only comic book movie I've enjoyed in a long time; although I've only seen Marvel movies lately. The last DC movie I saw was The Dark Knight Rises.
Anyway, I thought it was very entertaining and dark. It had more going on than the standard formula, and the fact that there was no hero on his tail trying to catch him or anything made it much more interesting. Joaquin Phoenix's performance was amazing as well; I think he's definitely tied or maybe even exceeded Heath Ledger's Joker performance.