It did make some changes to the book, primarily though not exclusively the ending. It also played up (ahem) a not so subtle Ho Yay element that wasn't really there in the original story if I recall correctly.

That said it's still a good movie. It stars Gandalf (!) (Ian McKellen) and he does a very good job. The kid is more disturbing in his evil in the movie than in the book.

Not the best adapatation of King's work but far from the worst.
FWIW, I think King liked it.

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.