It’s not common, but sometimes a movie can be better than a book. Clearer, more focused, or just reimagined.
Neverending Story by Michael Ende – The book drags on, including a war. The 1984 movie is a much more focused, clearer story. Incidentally the Neverending Story II (1990) and Neverending Story III (1994) are terrible. In my usual approach to my personal canon, I have decided they don’t exist.
(Sequels with rollerblades are terrible. 1985’s Return to Oz… rollerblades. Terrible.)
Do Androids Dream of Electric Sheep by Philip K. Dick / Blade Runner – The book is typical Philip K. Dick, which is to say weird, dense, hard to follow. The 1982 Blade Runner movie is much better.
Movie Different Than Book
It’s pretty hard to compare Jumanji by Chris Van Allsburg to the the 1995 movie, as Jumanji is a short kid’s picture book. The core ideas are in the book, but basically the entire storyline of the movie with the town and the kids is added. It made a pretty good movie.
Movies Adapted Into Books
This is a whole other universe that I will mention but not explore. Pretty much every major science fiction and fantasy movie that didn’t originate as a book has a book adaptation. Sometimes they illuminate or give a different view of the story. For example E.T. (E.T. the Extra-Terrestrial in his adventure on earth) by William Kotzwinkle in 1982 has rather more Dungeons and Dragons than you might expect. And continues into its own (not very good) 1985 sequel E.T. The Book of the Green Planet.
Also see previous post: Book Better Than Movie.