The Dark Knight is an amazing action packed ride that goes beyond the typical action film and draws you into the characters and story. Heath Ledger really is as good as everyone is saying. Overall a great film and a good story. I have only two criticisms of the film (no spoilers).
First, there are points in the film where Batman has a moral dilemma whether to kill the Joker. It's a moral equivalence arguement, i.e. if I kill the Joker I'm no better than him. Killing a murdering psychopath is not murder -it's justice, regardless of the circumstance.
Second Harvey Dent, the "white knight" district attorney who is a hero for going after the bad guys, has his own moral dilemma whether to take justice into his own hands. The arguement Batman (and others) use is that if Dent resorts to vigilantism, it will undo all his good work AND RESULT IN EVERYONE HE'S CONVICTED BEING SET FREE. It's an incredibly stupid arguement and reeks of political correctness (e.g. Don Imus entertains for years and raises millions of dollars for kids with cancer, but one joke of poor taste got him fired). It's just not how the law works and that arguement was very sophmoric and downright stupid.
Those two criticisms aside it's an amazing film and I was happy to see that the films creators wanted to interject some philosophy, even if they didn't always hit the mark (there were other philosophical arguements that I felt were closer to the truth).
So... go see it. Heath Ledger is amazing. Oscar performance.