Most of his best movies have largely been non-horror imho: The Shawshank Redemption, The Green Mile, The Running Man, Stand By Me, and Misery (sort of horror I guess) come to mind. The only horror movie inspired by his books that I really love is The Shining. He’s had several decent flicks, at least entertaining, including Silver Bullet (haven’t watched since I was a kid), 1408, IT, Cat’s Eye, Firestarter, Christine, Cujo, and Pet Sematary, but none of those are even close to the level of the previously mentioned films, again, in my opinion.
IT didn’t really require any crazy special effects until the very end, but they dropped the ball big time. I wish they would have just avoided showing us IT so vividly.