Two hours and 32 minutes long, "The Dark Knight" is grimly magisterial. It's a summer blockbuster that contemplates near-total civic disaster: Crowds surge, tractor-trailers flip, and buildings explode, but the pop violence feels heavy, mournful. Light barely escapes the film's gravitational pull.
Yet flitting through this 10-ton expressionist murk is a diseased butterfly with stringy hair and a maniacal giggle. Played by a dead actor, he's the most alive thing here.
It's not quite fair to say that the late Heath Ledger steals "The Dark Knight" from Christian Bale and the forces of (problematic) good, but, as the Joker, he is the movie's animating principle and anarchic spark - an unstoppable force colliding with the immovable objects of Batman and director Christopher Nolan's ambitions. Much more serious in intent and message than 2005's "Batman Begins," "Dark Knight" would be fatally ponderous without Ledger's nasty little sprite. As it is, the movie strains at its own Wagnerian seams.