I thought this was a very odd criticism from David Denby:
It’s a workable dramatic conflict, but only half the team can act it. Christian Bale has been effective in some films, but he’s a placid Bruce Wayne, a swank gent in Armani suits, with every hair in place. He’s more urgent as Batman, but he delivers all his lines in a hoarse voice, with an unvarying inflection.
Bale's performance in the film isn't as interesting as Heath Ledger's or Aaron Eckhardt's but he's "a placid Bruce Wayne" because Bruce Wayne is a placid guy, a character invented to disguise the identity of Batman. Similarly, Batman delivers all his lines in a hoarse voice, with an unvarying inflection, because he's trying to make his voice unrecognizable as Bruce Wayne's voice. Yes, it's weird to listen to. But why shouldn't it be weird to listen to a vigilante dressed in bat armor? The trouble with some of Batman's conversations is that, especially near the end of the film, he's speaking badly written dialogue -- nobody does ponderous exposition well.
The other thing I wanted to say was that while the praise Ledger has gotten is very much deserved, I'd appreciate some more acknowledgment that one reason he's able to do such an extraordinary job is that the Joker is one of the great pop characters. He, Batman, and Two Face, with the various different takes on them presented over the years, are great American myths, which is why their stories can be told and re-told over and over again in different ways to great effect. The Nolan/Ledger version of the Joker seems based on the Joker of The Killing Joke and A Death in the Family rather than springing ex nihilo from the filmmakers. Not that there's anything wrong with that, but it's worth acknowledging.