Between this thread and the other recent King thread, I'm discovering there is no consensus whatsoever on King's work. Some of my favorites (granted, from adolescence) have been mentioned as "worsts," including It, The Tommyknockers and The Stand. It would be hard for more recent books to outshine those ones (and The Drawing of the Three, Wastelands, and The Talisman) just because of the time of my life when I read them. You can't deny there's truth in the deconstructionist stance that a reading is an event, and a lot of influences other than the text factor into the impression that ends up in the reader's mind. I suspect there's a bit of a "Golden Age" effect at work in the way a lot of people elevate King's '70s/'80s novels.
Anyway, to the OP's question I'm with the others who singled out Dreamcatcher. Some King novels have left me scratching my head, not sure if I liked them (Insomnia, Rose Madder, Gerald's Game) but still thinking about them when I was done, and others have left me with the "Yeah, that was okay" feeling of a half-decent action flick or old pulp sci-fi novel (Cell, Under the Dome). With Dreamcatcher I'm not sure I even could have told you what it was about or named one of the characters a week later, at least until after I saw the movie. The movie was more coherent than the book, but still only achieved so-bad-it's-kind-of-good status.