There's nothing lightweight about 21 Grams. As in González Iñárritu's acclaimed Amores Perros, an automobile accident collides three different worlds. But here the wreckage is even more devastating, fracturing the very structure of the movie, which is all jagged details breaking through the blur. Like accident investigators, the audience has to pick up the pieces and figure out who, what, where and why. How does ex-con Jesus-freak Jack (Del Toro) connect with lapsing addict Cristina (Watts)? Is she even the same woman seen in happy family scenes? And why is Paul (Penn) an emergency in waiting? For a film devised in (mis)fits and false starts, much of this is surprisingly compelling. The director and his collaborators cook up a fervid spiritual battleground filtered through Rodrigo Prieto's intentionally cruddy camerawork - so low light and grainy it sometimes looks as if Paul's hair has turned green. The hand-me-down symbolism will appeal to those of a Roman Catholic disposition, but the movie is front-loaded with riveting angst. Watts is a revelation and Del Toro's sermon to his kids on turning the other cheek is some kind of stand-alone classic. Matters build to an almost unendurable a pitch of intense anguish. Unfortunately (if mercifully) this emotional peak occurs around the halfway mark. As the jigsaw puzzle fills out and the storytelling becomes more orthodox, the melodrama starts to strain. The director may want to scramble our sense of cause and effect, but when all's said and done, he still wants an ending, even the oldest in the book.