If Dark Knight gets anything right, it better be Two Face. Here's a hint at the grotesqueness to come.
Harvey Dent's character in The Long Halloween surely presents one of the more haunting depictions of Two-Face on a purely visual level. However, the payoff is weak: The villain emerges at the very end like a punctuation mark to the tragic vanity of Dent's attempts to cleanse the city of crime. However, Batman: The Animated Series truly allowed Two-Face to take on the frightening aspect of schizophrenic rage incarnate in a manner that bests your average Bruce Banner transformation even on average fucked up days.
The birth of Two-Face on The Animated Series took place over the course of two episodes, during which we learned that the vicious character arises from Dent's "Big Bad Harv" persona. If Two Face retains this element of eerie mental instability in The Dark Knight, we'll see one of hell of a horror film. Everyone gets that Batman is a creature of film noir; it's the loonies around him that give the procedural angle a terrifying twist. Bring on the depravity.