As with "Heart of Darkness" / "Apocalypse Now", this gets at one point I always bring up in these contexts: a book and movie can be related, but they are distinct works of art. (HoD/AN being an extreme example of distance.)
"The book was better" always strikes me as unhelpful. What is communicated visually is radically different than what is communicated in prose. Plus, an actor is an artist, too. "Here's Johnny!" cannot be achieved in text the way Nicholson delivered it on the screen.
King himself is standing too close to the prose work to assess whether the film is any good. Of course Kubric couldn't match a vision that exists in King's head.