Lord of the Rings and Hannibal Lecter movies for the exact same reason - the movies trimmed out all the meandering, annoying, unnecessary fat the novels had, which made the plot feel a lot more streamlined and better-organized in general.
The Shining - I'm glad Kubrick cut out of all the sappy family melodrama crap of Stephen King's book and completely focused on the more cold-blooded, mysterious, chilling aspects of the story.
Hellraiser - I didn't really like Clive Barker's The Hellbound Heart because it felt too manic and the story felt really cluttered and scrambled. But the movie's plot felt a lot more clear and focused.
Carrie - Brian DePalma's 1976 movie was so much more shocking and fiercely flamboyant and visceral than King's pedestrian first novel. It had the kitchen-crucifixion scene of that evil mother that the book didn't have.