If you read the comics at all, or ever liked the old Bill Bixby TV series, or just like really good action sequences, ala the Bourne Ultimatum, you'll probably really like this film. It far exceeded my expectations, and while it was not as good as the truly excellent Iron Man, I really enjoyed it. Minimal spoilers follow the image.
Banner has fled to Brazil to escape General Ross and the US Army, who want to extract what makes him the Hulk from and replicate it as a weapon. Bruce is lying low, learning to control his anger, and seeking help where he can to find a cure for his condition. He hasn't been home or seen Betty (Ross, his paramour) in years. Inevitably, he slips and the Army comes after him. What follows are some awesome chase scenes, a return to the US following his only hope for a cure, and a confrontation with the Army's newest Super-Soldier (c.f. Captain America's origin.)
In the end, the Hulk must face the Abomination, a Hulk-like creature spawned from the same weapons program that funded Banner's original research.