Quite fair to say The Dark Knight the most expert work of its kind.
Christian Bale continues as Bruce Wayne. Having eased into a lifestyle of excess, Wayne hides on the borders of his family corporation as CEO Lucius Fox runs the boardroom. But when Harvey Dent comes forward to challenge Gotham City's villainy through proper legal channels, the man also known as Batman sees an opportunity to replace his self-apponted character with a figure of virtue who will truly inspire the citizens.
Batman's success as a crime fighter has generated new problems for Gotham, including a consolidation of the crime lords who once controlled the city independently. Meanwhile, a new adversary named The Joker proves particularly dangerous because he seeks not only to advance the cause of Gotham's underworld, but obliterate the foundations of liberty and order that Batman protects. Torn between championing Dent and meting out justice as a masked vigilante, Wayne soon finds himself at a crossroads between being the hero that Gotham needs and the one it deserves.
An important idea of the movie is that Batman is not just a guy in a suit, but a symbol and The Joker want to destroy that symbol. While Batman's identity remains secret and his motives unknown to Gothamites, he represents hope in a city that has little to spare and imparts a pursuit of justice – and further, a code of behavior – that quite literally endangers these criminals' way of life. By throwing Gotham into chaos and testing the limits to which Batman holds himself, The Joker is not merely working with death and destruction but destroying the philosophical foundations of organized society.
Like few other mythology-based movies, The Dark Knight truly seems to think of everything, be it conceptual or purely logical. Credit Nolan and his brother Jonathan for really digging into Batman's world, turning over the soil and examining its roots for possible deficiencies. While this generally speaks to the film's rationality, they also have the presence of mind to consider such things as Lucius Fox's considerable monetary expenditures – not to mention his entire division – and how and where a paper trail might eventually lead to it. Again, however, these are not ideas or even subplots to which vast amounts of screen time are devoted, but simply revealed, explained and dealt with as they might arise in real life.
Bale is predictably effective as both Wayne and Batman this time around, playing both with greater assurance than in Batman Begins. Wayne is better defined and more poised character in this film – even when he's indulging the excesses of his trust fund – and he understands the value of being in a position to help someone like Dent. Also great is the rest of the original cast, all of whom seem as comfortable in their characters as if they'd created them themselves.
Meanwhile taking over for Katie Holmes, Gyllenhaal adds real depth and energy to Rachel Dawes, showing how her feelings for Bruce Wayne aren't simply not returned, but actually based in both sincere affection and common sense. And Eckhart more or less combines all of the disparate roles he's played in the past into one seamless portrayal of a man determined to make things better but not quite sure how to accomplish that goal in the right way.
Finally, Ledger, whose performance will be the subject of many analyses of all sorts in the weeks and months to come. What he does with The Joker is, quite frankly, nothing short of crossing all the normal human experience. Early in the film he explains the origins of his scars, and you worry for a moment that the filmmakers are giving this psychopath some kind of convenient explanation, which, talented though he was, Ledger won't be able to overcome. But by the third time he's explained where they come from – each time telling a different tale – you realize that Ledger was a master of his craft, only in his final years finding roles that truly offered him the chance to explore that mastery. He is the unanimous movie Joker, and he owns the role and achieves a level of prideless insanity that is terrifying as it is irresistible.
Overall, what happens in a story must be surprising but expected, and Nolan's approach to The Dark Knight epitomizes this truth. He gives you exactly what you want, but does it so well that it manages to completely catch you off guard when it happens. But there really is no better way to describe The Dark Knight than to call it a great work of art because it crosses the boundaries of both comic book moviemaking and even the parameters of great filmmaking.