I've read about two-thirds of his work. I think "The Langoliers" is the best thing he's written, and by far his best ending. I also love his collection of novellas called "Full Dark No Stars," which has a couple of stories with no supernatural elements. I think he's at his best when he sticks to reality.
My favorite novel of his is "The Long Walk." As far as recent work, "The Institute" is the best thing he's written in a while.