In the past, Batman movies can be enjoyed by the whole family. This new Batman, The Dark Knight, is not suitable for children, in my opinion. Two-Face, although the make-up is great, looks very scary. In the beginning of the movie, when I saw how handsome Aaron Eckhart was, I almost couldn't imagine what he would look like when he became Two-Face. It's sad he dies in the end, because it means no more Two-Face in the next Batman movie.
Perhaps it's because Christopher Nolan directed this, that the movie becomes so dark. It does connect to the title, though. The handsome Harvey Dent is the White Knight of Gotham, while Batman is the Dark Knight.
The Joker is a sick character. True, he is a freak, but how freak the script has made him is also a scary process. In the beginning of the movie, we see that Joker doesn't trust anybody. None can guess what he thinks, what his goal is, except that he works without rules and that he enjoys making people panic. The code of honour among criminals/thieves is not applied to Joker. In the first robbery scene, we see how Joker's thugs kill each other because of greed.
The voice of Batman is a bit disturbing. I understand it's to show the audience how the people who know Bruce Wayne's voice don't recognize his when he becomes Batman. The suit must have something to distort the voice.