This gets good marks simply because it is such an interesting, involving story that hooks you right away and every time you watch it and doesn't overwhelm you with violence and gore.

Denzel Washington is appealing as always as the good guy and John Goodman is surprisingly low-key for most of the movie. All the characters are very interesting and the special effects are creepy.

The story is pure "Hollywood theology" mean also means the characters - include the heroes - in here have no clue about God or the purpose of life. Believability-aside, it film provides excellent entertainment. The visuals are decent and sound-effects are chilling in spots. As the demon sees through the eyes of people and passes by with these "whoosh" sounds, it's very effective. As mentioned, the film doesn't need a lot of violence to succeed with it's horror-type tale.

One note about the final scene. It isn't exactly clear on a couple of points so if you get confused, you aren't alone.