Music

 Graphics, detail, scenery, location, acting, ambient lighting. All of these are important when relating to a film, whether it be a movie or a documentary, or even an indie film production. However, of all the the things that go into a video, the most important has to be the soundtrack. A great movie is determined by how much it can move its audience. And in a culture as music-centric as our own, having a great soundtrack that moves you right down to your core, can make the difference between having a good film, and a brilliant film. The video linked in this post is one of the more modern genres known as "dub step." A type of beat-centric trance music.  This, is an example of a good theme to use in a film, if say, you were going for an emotional fight scene, or a travelling montage.
Fact of the matter is, good music can make, or break, a film. And can be the deciding factor between whether it becomes a blockbuster, or a one hit wonder.