4. Rambo
Film adaptations of novels always require alterations in order to make the story work in a cinematic format. Sometimes, even the ending is changed so that the film will be more palatable to the audience. In the case of the first Rambo movie, its source novel First Blood ends with the death of the protagonist. This ending was filmed but a test audience apparently found it too depressing. Sylvester Stallone agreed and a new ending in which Rambo survives was shot. Given the quality of the later Rambo films, the test audience probably should have thought twice before they rejected the original ending: http://www.youtube.com/watch?v=bn187skbynQ