My comments (some spoilers)

Overall, it was way better than I thought it would be. And even then it was still pretty good. Of course, there were parts that were hilaariously bad, where I actually laughed aloud, but they didnt't ruin the movie per se.
I was not surprised to see Paul Bettany do his usual surly, gravelly-voiced vigilante hero bit that he always does. He didn't do a bad job, but then again it's the only role he can successfully play. He did ok at showing emotion, the bare minimal, when it was necessary, and it wasn't his fault when he had to work with awkward lines, so I didn't really have a problem with that aspect.
I don't know if they did this on purpose or not: the few actors in it that played humans but have played vampires in previous things (Stephen Moyer, Cam Gigandet). If they did this on purpose, then that casting decision makes me cringe. I kept expecting Kate Beckinsale (Selene from Underworld) to show up with a cross tattoo on her forehead. That seems a shallow idea for filmmakers to make. Stephen Moyer (played the priest's brother in this movie, played the vampire Bill in True Blood) posesses some credible acting skills, but Cam Gigandet (Hicks in this movie, James in Twilight) struggled heavily in this film. I actually thought he did a great job as James, and his acting isn't usually too deplorable, but in Priest, when his character was so cliche it was ridiculous and his lines were even worse, it was somewhat painful.
The movie itself, scenery wise, reminded me of a mix of Star Wars, Blade Runner, The Matrix, and Underworld. The special effects were really impressive, and I enjoyed the contrast between the brightness of daylight (which at points actually hurt my eyes) and the gray darkness of night. I felt like there was some decent symbolism in there. The movie, for a relatively short film (for its genre) did a good job of presenting the plot, situation, and backstory with a small amount of time. I knew everything that was going on, and it wasn't too hard to decipher what had happened to the world. Some movies, like Inception, are more enjoyable when you're not entirely sure what is going down, but action movies such as this need to be concise in order to keep audience's attention. It was somewhat predictable (my dad and I predicted that his niece was actually his daughter quite a bit before it was revealed; that's an overrused storyline), but it was definitely worth a watch, and I wouldn't mind there being a sequel.