Fucking great movie. To be honest, I feel the Ledger performance is overrated. Now, I'm an Australian, so I have a national pride in the man for kicking ass, and The Joker did kick-ass (the pencil trick was the first time I heard anyone applaud in a movie cinema), but I think a character like The Joker is a) way too fun to fuck up, and b) has such great writing and ambiance behind it. I don't want to sell Ledger short. Great performance, and a crazy fun villain, but I don't think he deserves an Oscar, especially when I feel that there were actually stronger performances (substance-wise, if not style-wise) in the movie.
Aaron Eckhart was fucking incredible. Harvey Dent was an amazing character. Everything about him was in perfect tone. I loved the emphasis they placed early on Dent being right handed, only to have Two-Face become a lefty. That was great shit. I loved the way he went above and beyond as Gotham's DA. The scene where the cops were applauding him as he was getting into the back of the truck was just so cool, in my opinion.
Aaron Eckhart deserves just as much kudos as Ledger, in my opinion. His scenes in the hospital were great. He gave me a legit scare several times. Horrifying stuff. I also love the dark twist on the Two-Face character.
I personally feel they should bring The Joker character back. Heath Ledger breathed such a good life into the character that it shouldn't just be discarded. Johnny Depp taking over would be fantastic, but one idea I would have to suggest is that Jake Gyllenhall get the role. He's a tremendous young actor, and he's good friends with Heath Ledger. His sister was also in the previous movie. It'd feel more like a tribute to Heath than an insult to have Jake take over the role. He's talented enough to get the best out of it, too.
Depp would make a fantastic Riddler, or something. Isn't he rumoured to be the villain in the next one? I've also read some people who theorize that Bane was the big black guy on the boat, and that Two-Face is still alive. I have several theories about Two-Face:
The first is that he is dead, simply because I can't think of where the character could go. He was awesome and everything, but the transformation was what worked so great about it. By the end of the movie, Two-Face was just flipping a coin and shooting people. Yeah, it was cool when he shot the driver after putting on his seat belt, but he's got no power anymore. Dent dying does seem like a fitting end to the movie.
On the other, the movie was perfectly constructed. The direction was nigh-perfect, and I have to ask why Batman fell from the same height Dent did if not to show that it is possible to fall from that height and survive? Maybe they just felt like having a scene by the edge of the water, or something, but I can't see Nolan including that little detail for no reason other than to prove that it is possible Dent was not killed by the fall.
It'll be interesting to see what does happen, because you have to believe that there will be a third if Nolan wants, considering The Dark Knight has done so well.
The next movie should probably take plot points from The Dark Knight Returns. Instead of being set in the distant future, I can see it just being a few years down the track. Gotham is in a state of chaos, with a new villain running things (Bane?). Harvey Dent survived his fall, but there was a cover-up into his death, but he has accepted surgery and can now be the hero Gotham needs. The Joker is laying dormant at Arkham, and is convincing his young, female psychiatrist that he is cured. I could also see the Selina Kyle character being introduced, and inspired by Batman to become The Catwoman.