Ordinarily, comic book movies are an exercise in the aggressive non-suspension of disbelief, for me. Whether internally criticizing absurd physics or ludicrous plot points, I generally entertain myself more despite them than through them. The Dark Knight was an exception.
I posit two major reasons for this. Firstly, it is a result of the character of the Batman universe. It exists at a larger scale than many fictional or comic universes and, as such, has more freedom to establish its own rules and expectations. It is much more Lord of the Rings than Spiderman, despite greater superficial similarities with the former. Gotham City simply differs enough from our world to make it a clear allegory, rather than reality with implausible supernatural additions and equally implausible smoothing over of plot progression (How do characters put things in place to appear at the middle of chaotic chase scenes? How does the Joker recruit and train people? Why can everyone use unfamiliar equipment instantly? Etc.) It takes a pretty good film to suppress such questions in my mind, and this one manages it notably well.
The second is simply that the acting and presentation are quite compelling. The over-the-top action sequences are less asinine than in many smasher films, and there are some decent character and thematic issues addressed. Probably more importantly, the film has a powerful aesthetic – one that even a fairly reluctant appreciator of alternative universes can respect. Where the later X-Men films felt tacky and emotionally overdone, the gritty and chaotic Batman style remains stubbornly consistent.
Of course, Batman’s moral code remains ludicrous. Simply refraining from actually killing people immediately and with your own hand seems like a bizarre form of self-limitation, when you are perfectly happy to set off massive explosions and otherwise indirectly kill large numbers of people. The film isn’t entirely divorced from point-scoring on contemporary political issues (such as the security value of mass surveillance), but it wears such garments in an accessory fashion, rather than serving as a vehicle for polemic.
On a side note, the film demonstrates the degree to which Hong Kong is itself an alternate universe, at least as viewed from the air. The place looks like Ghost in the Shell made flesh, and provides an almost visceral reminder of the rise of Asia – one that the upcoming Beijing Olympics will doubtless reinforce.