I think one of the problem's with the voice is that it sounds forced, not practiced.
That's probably the most apt criticism of the Bat voice I've heard. You can hear the effort Bale has in giving every syllable in each word - it's distracting.
Two-face doesn't really work. The justification for his coin-flipping philosophy from the comic book character never is explained very convincingly.
This, entirely. I'm more then willing to give the film a pass for the Joker staging implausible or even downright impossible plots - this is pretty much the norm not just for comic books, but action summer blockbusters in general. Nolan's Batman movies are realistic in the sense the Die Hard films are realistic (although judging by Live Free, they probably aim for greater plausibility).
But the thing one expects as given from a comic book movie is motivation. Your villain has his reasons for doing what he does, even if it is, as with Heath Ledger's Joker, just to watch the world burn. Harvey Dent delivers an about-face (ha ha I make funny) that is far too abrupt given what we've seen of the character to date.
People buy it not because it makes sense in the movie, but because it's Two-Face - they'll all expecting him to go nuts and start coin tossing the moment he gets the symbolic charring of half of his face. It fits the checklist but not the narrative.
And as far as comic book movies go (mainly, I mean to say superhero movies), most aren't going to be as good as (or better than) THE DARK KNIGHT.
History of Violence wasn't bad either. And I got a soft spot for Persepolis.
But yeah, the Dark Knight is really a stellar bit of blockbuster moviemaking and storytelling. Wouldn't be surprised if it remains the gold standard for some time, and the biggest fear Batman 3 is going to have is living up to that ungoldly hype... but then, Dark Knight had a bucketload of hype paving its routes as well.