As a horror movie this movie is actually kind of bad. It's neither scary nor suspenseful. However, as a comic book adaptation, it's a great movie. In fact I'm almost inclined to say that the movie is better than the series it was based on.
The movie is based on issues 1-3 and does a great job bringing to life the illustrations in the original comics with the cinematography imitating the original coloring, shading and lighting used in the comics.
Also, ironically, I think as an actor, Josh Hartnett gives the best performance of his career.
If you are a fan of comic books and are mildly unimpressed with the recent movie adaptations, this movie is for you. But if you are a horror fan especially of the vampire genre, you may be dissappointed