Good article on Commentaries: What Is a Good Christian Movie, Anyway? (Part 1) - Christianity Today Movies:
Now this might look like a simplistic question. But it is important to know not only what a thing is, but what it is not. Succinctly put, a movie is the art of storytelling by way of motion pictures. A movie is not a sermon. A common mistake in the Christian community is to confuse sermonizing for storytelling. Desperate to convince the prodigal son, the Christian producer employs the instruments of film in the service of propaganda: the propositional persuasion of the viewer toward an idea.