Just in case you missed the trailer:
Overall, I liked it. Originally based on a graphic novel, the film mostly followed the original with a few twists.
It's survival horror; less about an unstoppable monster killing those who violate moral rules and more about people dealing with horrific events.
It's also a vampire film. The vampires here, however, aren't effete dandies who are overtly gay, nor are they bratty rich farts with a taste for blood.
The portrayal of vampires in 30 days isn't remotely likable, nor is it remotely human. I didn't get the impression that these were humans who had become monsters, but rather that they were monsters who looked a bit human.