Jennifer Lechner suggested this list well before I saw Shutter Island last week, and although I'll post five suggestions of my own here, this is a topic better suited to a long, wine-enhanced conversation around a dinner table.
For one thing, what makes a good adaptation? Someone who loves a book will reject a movie adaptation that isn't faithful enough, or whose characters don't look the way the reader imagined. Some movies are extremely faithful to their source material, but at the cost of feeling less like a movie than a book-on-video (I'd put most of the Harry Potter films in this category). And of course you can't even have this conversation unless you've read the book the movie comes from, which — if the movie's good enough — people may not have any reason to do.
So for what it's worth, here are five films I found more entertaining than the books they came from. Leave your own opinions in the comments section, or feel free to disagree.
1. Jaws, 1975. Screenplay by Peter Benchley and Carl Gottlieb, from the novel by Peter Benchley. Jaws has to top this list; in fact, it's almost a classroom example of the relative strengths of film and print. Where the book had to explain and describe, the movie could just show, and that's important for any thriller, especially monster movies. (And yes, although the shark in Jaws is real, it's still a monster movie.)
2. Sideways, 2004. Screenplay by Alexander Payne and Jim Taylor, from the novel by Rex Pickett. I was so charmed by the film that I read the book, and wished I hadn't. For better or worse, actors and their directors have to find a way to make viewers care about a movie's characters, while authors can write about rotten human beings and call it satire or social commentary or literature. We might be willing to read a book about a person we dislike, but we're not willing to watch a movie about one. Paul Giamatti and Alexander Payne allow us to identify with the central character of Miles, while Rex Pickett's book only lets us despise him.
3. The Godfather, 1972. Screenplay by Mario Puzo and Francis Ford Coppola, from the novel by Mario Puzo. I'm not sure I've read this entire book. If memory serves, my fifth grade class passed a copy around for the purposes of reading one particularly lurid sex scene; we did the same with Jaws, which I read in its entirety. But my memory of the book of The Godfather is of a narrative that was just too big for a book, with too many characters and too much to keep track of. Coppola's genius was his ability to pull out the central stories and turn them into two epic movies; we're so entertained that we don't even realize how complex the story is.
4. Runaway Jury, 2003. Screenplay by Brian Koppelman & David Levien and Rick Cleveland and Matthew Chapman, with uncredited material by Caroline Case and Scott Rosenberg, from the novel by John Grisham. The book is about a criminal negligence suit against a tobacco company; the movie transposes it to the gun industry, which was more timely when the movie was made and also somehow feels less self-righteous. The movie does a better job than the book did of concealing the main characters' true motives, and the secondary characters are vivid on screen, while some verge on caricature in the book. At two hours and seven minutes, the movie's also faster-paced than the 560-page book. (Full disclosure: the movie's director, Gary Fleder, is one of my oldest and closest friends. This movie would make my list anyway.)
5. Stand by Me, 1986. Screenplay by Raynold Gideon & Bruce A. Evans, from the novella "The Body" by Stephen King. "The Body" is a fine novella, part of King's excellent collection Different Seasons. Stand by Me takes that material and turns it from entertainment into art. The film compresses and condenses the print narrative, and brings the story an immediacy the print version can't have. "The Body" is told as memoir, but Stand by Me gives us the story as the boys experience it, using a framing device to show us that it's a remembered and possibly idealized version of events.