I read this because of the sequel that's due out later this year. Very much the same as the film except the ending which I won't tell you about, you'll just have to go read the book, it's actually entirely different and a much more satisfying ending in my view.
The slow creep of madness and ratcheting up of desperation and terror is felt much more deeply over the course of the novel than the film I thought. I really enjoyed this.
Excellent stuff. Can't wait for Doctor Sleep.