The thing that most impressed me is the way that Gotham itself returns as a character and a stake in the film, where Tim Burton had reduced it to little more than a style. For much of the Batman we've seen on screen, the Caped Crusader has had enemies, and saving the city was reduced to saving large numbers of citizens from death by a million penguins, insanity, freeze-drying (please don't think less of me if I acknowledge that I've not seen more than fifteen minutes of the screen time of Batman and Robin), or some such.
In Batman Begins, this begins to be reconceived. Bruce Wayne cherishes the memory of his parents as citizens, and part of the drive that at once pushes him to become the vigilante Batman but also to obey certain limits is his desire to reclaim the city, which Ra's al-Ghul sees as a decadent thing that needs to be put down. Bruce Wayne doesn't become Batman by running around in a costume trying to heal the personal loss of his parents by chasing the guy who did it and then everyone who vaguely reminds him of that thug: there's no doubt that he is deeply afflicted by their loss, but part of what makes him a loving son is that he understands the sense in which Gotham lost his parents. The risk he's running to his own sanity isn't that he's using an alter ego to repeat something that he's never going to set right but that he refuses himself a normal life until he believes that Gotham has been saved, even as that denial of his other needs and desires eats away at him to the point that Bruce Wayne may become the supplement, the shadow of Batman rather than the other way round.
Batman's battle with the Joker in this film is a battle for that elusive thing, the spirit of the city, the polis itself as the essential political entity, and one is sees here profound parallels with the time in which it was made. If Batman Begins was about fear, The Dark Knight is about terror. The Joker knows how the threat of violence can change people and how terror can change a community, and the calculating side to him understands how to make monsters, small and large, out of people, however upstanding. He understands the changes to the city that Batman has set in motion and how to threaten them with radical reversal, but he also understands that even the logic of these threats must defy and exceed expectations: he threatens to do the worst and then does worse yet.
Batman, on the other hand, understands his own exceptionalism as a self-appointed agent of justice, without the slightest sympathy for those who mistake him for a generalizable example, whom he treats as criminals no different from the rest. He understands that to restore the city, normalcy is critical and therefore desires justice to be reduced to the uncorrupted rule of law, which is not what Batman can himself produce. As Bruce Wayne, he is therefore unvarnished in his admiration for Gotham's other crusader: District Attorney Harvey Dent quickly becomes his hero and hope for the future, a man who goes without a mask, without fear into the open to challenge criminals and even allows him to imagine a future where he can just be Bruce Wayne, who can then resume his romance with Rachel Dawes (who duly admonishes him, "Bruce, don't make me your only hope for a normal life.").
Let there be no doubt: the film has its weaknesses. Michael Caine's Alfred is lost to didacticism, despite moments of humour. In the last big action scene in the movie, I got completely lost in the edits. The wheels come off the Harvey Dent drama about three-quarters of the way through, and despite some attempts to recover with well-conceived remarks about the ability of chance to foil the vanity of human design, this is perhaps the most significant disappointment of the film, with Aaron Eckhart's performance given far less attention than Heath Ledger's as the Joker, which has attracted so much well-deserved commendation that I can add no more.
Gotham is not the backdrop to this movie over which Joker and Batman battle: it is both the ground and stake of their battle. You don't have to imagine that Nolan used Baudrillard's Spirit of Terrorism or Agamben's State of Exception as research materials for this film (although the reference to the Roman dictators make you wonder about the last), but this film drives home again that such are the stakes of our times and that we understand this better than we often acknowledge in more conventional political discourse.