Six movies and a videogame into the franchise, and nobody still has any idea what the hell is going on.
Cracked on Saw
Saw is about a guy, John Kramer, who is dying... or dead or something. In the beginning, after failing to kill himself, he decides he would probably be better off killing others. He becomes so content with this idea that--even AFTER dying--he continues offing people for three more movies and a videogame. His kills thus far include his hot assistant, a couple of doctors, one of the movie's writers, two guys from Lost, one the the New Kids on the Block and a cop who is getting too old for this shit.
The movies are notorious for their sick, twist endings, that creepy little puppet and a total lack of a coherent storyline.