I've said this before, in other places, but I have to mention again: Stephen King's Pet Sematary
is the best horror novel I've ever read. Once it gets going I can only read for about twenty minutes at a time before I have to stop and shiver to myself for a while.
I hate to be trite, but I think it works because it's about decent people doing terrible things. You, the reader, know that the Pet Sematary is evil. So does everyone in the story. But things get buried there, all the same, and huge swathes of the book are characters persuading themselves that this time will be different. Reading it is an incredible effort, painful and pleasant at the same time. It's revolting, but addictive. I always hated that kind of dramatic irony, where we're watching the characters careen toward destruction, but it's got an undeniable power in King's hands. I'm not a big fan of the climax, but the last page is perfect.
To quote Gene Wolfe, yet again: "Life, after all, is not a high thing, and in many ways is the reverse of purity. I am wise now, if not much older, and I know it is better to have all things, high and low, than to have the high only." Pet Sematary
is unquestionably a low thing. It evokes feelings of dread that seem to bypass the brain completely, and it's very close to physically painful, but I can't pull myself away.