On the whole, I liked the movie and was entertained. The first hour and fifteen minutes or so was really funny, but the last 30 minutes or thereabouts was completely absurd. Nothing I would watch in the theater, but it would be worth a rental for a few chuckles.
I don't want to give anything away, but the movie is practically flawless. If Heath Ledger doesn't win a posthumous Oscar for his portrayal of The Joker, there is something wrong with the Academy.