I've read probably 90% of everything he published.

IT is definitely up there. I feel like a lot of the others were probably a lot more shocking at the time they came out, which was before my time.

King's grandest opus is the Dark Tower, especially the former half of the collection, but ALSO all the other books and stories that tie in with that universe (like Insomnia etc). I'm also an avid reader of his short stories, some of which are more bizarre and 'special' than his full feature works. Plenty of those have spawned decent movies or series in their own right (and some failed miserably, but not due to King's writing).