I totally understand why no one really likes this movie. The plot is murky, told in flashback from a mentally disabled person. The satirical jabs at the art community and the nature of celebrity seem tacked-on, and the core mystery of the film is pretty easy to figure out.
But then you have to consider the dream-like mood of the entire piece, the performances of the actors who go above and beyond, trying to sell the preposterous story (seriously, this is one of Mel Gibson's better performances), and the interesting mish-mash of people who wander in front of the camera (Bud Court, Amanda Plummer, Donal Logue just to name a few). There are fragments of a million good movies in here, mixed up togther into a mosaic that almost, but not quite, achieves greatness.