Daybreakers concerns a not so distant future where Vampires are the dominant species and humans are hunted like animals, and even farmed for their blood. But the supply of humans is dwindling, and a researcher, Dalton (played by Ethan Hawke) is trying desperately to come up with some kind of synthetic blood as a replacement, as some vampires have begun feeding off of themselves and are mutating into horrible, disgusting creatures. When Dalton meets Elvis (Willem Dafoe), Elvis recounts how, through an accident and precise series of events following that accident, returned to humanity from being a vampire, Dalton feels like he may have found the cure for the Vampires problems.
Daybreakers isn't awful, it just isn't very good. The plot is interesting enough, but its wrapped up in so much "wouldn't it be cool if" that it becomes a well funded B movie that just happens to star A-List actors. It comes off as the kind of film that everyone probably thought was a good idea, but just didn't turn out that way. Unless you're super into Vampires, I wouldn't bother.