The book is better than the movie.
Much, much, much better. And you should know that I love the movie. The book just has so much more character to it; there are layers upon layers of author and editorial notes that tell a story of their own. You can't quite distinguish reality from the fiction, and that's one of the points of the book. There's also background and history and context like you wouldn't believe. Ever wondered WHY Fezzik had a holocaust cloak? Read the book.
Just read it. I was lucky enough to read this in high school as an assignment. Part of one of my exams was to write a "reunion scene" for the end of the book - I still think it was one of the best things I ever wrote.
Read it and enjoy.