First off, thank God Katie dropped out and Maggie stepped in. She was a definite plus in the film and was 20 times more believable.
Everyone has heard about Heath Ledger's performance which is truly unique and disturbing but Aaron Eckhart should also get a lot of kudos for giving a great performance. The people steering the ship should not forget Christian Bale! He's a great actor and the lines he had to work with in this movie were not in keeping with that. A lesser performer couldn't have pulled it off.