Huge Stephen King nerd here. Read the book twice, listened to it twice. It's not my favorite, but it's worthy for many reasons.
With few exceptions, (Green Mile, Misery) King's adaptations to film fall short. This is another exception. You like the book? You'll love the film. I enjoy it because the casting was stellar and I can nerd out about how they nailed it. I just never get to see the vital essence of the book in film. It scratches that itch.
Again, they nailed the acting and story. It's small repayment for the Dark Tower fiasco (I literally cried in the theater), but we Constant Readers take it where we can get it.