You're gonna be bothered by how cool I am.

The writer builds the framework, the director sets up the shots, and the actors bring the story to life. But the people who quite possibly wield the most influence over the finished film are the editor and the film's composer/music supervisor. Just look at these three entries in a recent competition a post-production house organized in which assistant editors were challenged to "re-cut" trailers from different movies to make them seem like different movies.

West Side Story
Titanic
The Shining (*winner*)

The West Side Story one is a bit of a cheat, because the editor has added things to the film clips, but The Shining one is AWESOME!