Oh, don't even get me started on Stephen King. I can't stand the guy's stuff, either in writing or, normally, on film. But I love Carrie, for reasons that may some day become clear if I ever finish writing my ponderous review of it. There's more to that movie than meets the eye. But even what meets the eye is impressive. The whole drenched-in-blood thing, that creepy wide-eyed stare, Carrie wandering dazed down the street, trailing burning buildings behind her...maybe you should watch it again if you haven't seen it lately to remind yourself just how much contemporary horror owes to that movie. Or maybe not. I'm not saying you don't have a right to your opinion, but...well, I'll put it this way: I'm not a huge fan of Psycho, but I'd never deny that it's a great and hugely influential horror movie.
To me, I felt that whatever Demon lived inside King fled at some point. It may be as simple as he lost his edge as he got older and fatter and wealthier. I loved his early stuff: Carrie, The Shining, Salem's Lot, The Stand, etc--his later stuff became a little hit or miss in my opinion.I thought what he did that was so great was his characters--he actually created characters that you liked and then fucked them up, instead of just fucking up cardboard characters that you don't really care about or you're actually glad to see killed--modern film-makers and writers can still learn that lesson. Maybe it was getting run over by the van that caused him to mellow (it sure caused him to fuck the dark tower stories up), but I think he was already changing.
I can't blame him for the movies--he just wrote the books, but I will give him complete credit for being the driving force behind making Horror popular and marketable again and allowing Horror writers to actually make a living at their craft.
It reminds me of something Elvis Costello said in an interview when asked why he didn't write angry songs anymore. He said, "I used to write angry songs when I was an angry young man--now I'm a rich old happy fat man, so I write happier songs now."