I think I've said it plenty of times before, but I've never quite gotten into the whole Vampire thing even before Twilight had movies. I remember people in High School around 2000 making a big deal out of Vampire: The Masquerade and other such junk. To me, it seemed as if they were all missing the point. Vampires weren't supposed to be a great thing, but a bad. Any benefits are lost with your humanity, in addition to a few other problems such as exploding in sunlight.
Daybreakers drags vampires back to where they belong (well, I guess where modern vampirism belongs, as opposed to the original tales of pure fear that actually spawned them). Sure, everyone is immortal, but life isn't actually better. In fact, life seems worse if anything else, especially with the human population slowly running out.
The film feels as if it moves slowly, even though technically events roll by at a steady and swift pace. It is bloody, but you don't get much worse than gallons and gallons of blood. The action is good, the plot is told well, the directors know how to make viewers jump and the third act unfolds in an excellent "ah-ha!" manner.
It's a vampire film that ought to be seen, much like Interview with a Vampire.
Incidentally, I've noted a few people viewing the shortage of humans as a tie to the depleting resources of oil, but I had seen another though possibly unintentional metaphor. At the start of the film it seems as if the majority of vampires smoke. In fact, the initial business meeting everyone in the room has a cigarette or cigar in hand. Later, as blood begins to short, a horde of people practically attack a stand of blood-laced coffee desperate for sustenance.
It reminded me of addiction, really. Be it cigarettes, drugs, or even an addiction to over-eating, these are all things that we think deride pleasure. However, when you go without it life is absolutely terrible, depressing, and all the negative things of the rainbow. The addiction becomes a necessity to live.
Here we have vampirism, reliant upon human blood, offering people to live without fear of cancer or death. But the cost is the inability to survive in sunlight, a reliance on a finite source of sustenance, the lack of which literally turns you into an animal, and basically a complete lack of freedom.
At the same time, a draw can also be made to what people will do in order to escape mortality.
Overall, it's a vampire movie that actually makes you think of what such an existence would mean, instead of being fetishistic upon the good while ignoring all evil (I'm looking at you shitty series of books of sparkling abstinence vampires).

