Part of it was the Dark Knight, which, to be honest is my favourite portrayal of him that I've seen so far. He's clever, resourceful, merciless, manipulative, cruel and enigmatic. But most importantly, he has a point to prove, rather than the standard villain who goes for money and/or power. He's also ironic in a way, that in trying to prove that the Batman is just as corruptible as the rest of us, he helps prove the opposite when Batman takes the fall for Harvey's crimes so that people won't lose hope. That's my opinion, anyways.