It's okay for a film to modify a book a little for the sake of the medium. Heck, if they madeA Tale of Two Cities into a movie today we'd expect at least 10 explosions and a hostage standoff. But in the case of some sci-fi films, the book's ending was completely thrown out in favor of a new plot twist.
We took a look back at the most radical book-to-film ending changes, and determined if they were better or worse than the original conclusion. LINK