Tuln, the Joker as presented by Nolan was way to one dimensional and missed out on a truely insane, warped world view Joker that could have been. I only felt he really captured the Joker once in the whole movie and thats when he pushed the button and the hospital didnt fully explode.
Two parts added in would have made things better for the character.
Scene One when the commisioner was killed drinking the poisoned liquor he should have died laughing and and with the Joker smile on his face.
Scene Two when the cops lifted the shirt of the guy with the bomb sewn into him, it should have been put in like a clown face with the blinking light as the clowns nose.