Catching Fire
Based on: Catching Fire by Suzanne Collins
While the book focused on the clothes, the hairstyles and the politics between the victors, the movie focused on the relationships between the Katniss and those closest to her, while delivering amazing action scenes.
The Lord of the Rings
Based on: The Lord of the Rings series by J. R. R. Tolkien
Don't get me wrong, the books are a masterpiece in world-building — the gold standard, in fact — but that is what they mostly are... worldbuilding. We get 2 pages describing a single building, and another 5 pages describing Mirkwood — dry slogs with action and entertainment interspersed. Worldbuilding should be in proportion to character development and plot. In this way, the films are far superior — not only were they well-written and directed — they didn't get bogged down in detail.
Howl's Moving Castle
Based on: Howl's Moving Castle by Dianna Wynne Jones
While Dianna Wynne Jones' provided so many classic moments, Miyazaki's film simply came alive with his visuals and the music by Joe Hisaishi. The movie took on a more mature feel with the inclusion of the bombing scenes and had more to say about war, suffering and perseverance — the book borrowed elements in absurdism; plot is almost circular with the characters not learning much in the end. Also, the book provided a lot of detail on Sophie's relationship with her sister, while the movie focused on Sophie and Howl's personal and relationship growth. However, Miyazaki's ending became a deus ex machina ending with potato-head's true identity; Dianna Wynne Jones' book set this up in advance.
Blade Runner
Based on: Do Androids Dream of Electric Sheep by Philip K. Dick
Philip K. Dick's novel had a lot of big ideas struggle to translate into an active, passionately-told story. The novel's character also felt underdeveloped characters without sufficient backstory, while Harrison Ford brought the character to life, giving the story an emotional core, drive and purpose. The film the cornerstone for sci-fi detective noir films, while the book needed to throw itself fully into the detective/thriller genre, rather than dally on the outskirts.
Mean Girls
Based on: Queen Bees and Wannabees
Queen Bees and Wannabes is a 2002 self-help book by Rosalind Wiseman. It focuses on the ways in which girls in high schools form cliques, and on patterns of aggressive teen girl behaviour and how to deal with them. The movie was hilarious, heart-warming and in the end helpful to girls dealing with nasty school cliques.
The Godfather
Based on: The Godfather by Mario Puzo
The first Godfather film was meticulous, terrifying and slow-burning; the characters came alive with amazing performances by Marlon Brando and Al Pachino. The book contains very *ahem* vital sub-plots of Sonny's giant manhood and his girlfirend's giant womanhood (which a doctor rebuilds and then tests himself). No. I'm not making this up.
The Prestige
Based on: The Prestige by Christopher Priest
The book was good, but the movie was simply amazing in the hands on director Christopher Nolan. While the book used actual ghosts for the magic, Nolan relied on future technology and the simple trick of twin brothers.
Fight Club
Based on: Fight Club by Chuck Palahniuk
Author Chuck Palahniuk admitted that the film was better than the book. Not only did we get stunning performances from Brad Pitt and Edward Norton, the "twist" in the end of the plot is more surprising when done in film than in books -- no one would suspect Pitt and Norton to be playing the same character.
The Devil Wears Prada
Based on: The Devil Wears Prada by Lauren Weisberger
Fashion is a visual medium; having costumes on-screen works much better than having garments, their colour, texture and shine just described in words. Now only did we get to see the fashion in the movie, the villain of the story, Miranda Priestly, was brought alive by Meryl Streep who added more emotional depth to the character than what was granted to the character in the book.
The Mist
Based on: The Mist by Stephen King
Even the man himself, Stephen King, said that he prefer the ending to The Mist in the film than in his own novel. The film found a darker ending the King's original story. King himself regularly admits that writing endings to his book is his biggest downfall.
Children of Men
Based on: The Children of Men by P. D. James
The book is dark, but the film is darker; if it is one thing which I admire about the film is how the background of each film set tells a story — you can watch a video explaining the concept more here. Simply put, the way the background is used in the film is something which cannot be done in a book.
Eragon
Based on: Eragon by Christopher Paolini
Haha. Just kidding.