We live in a world of finite resources. Everything, from water to real estate to energy to even creativity will run out/become poisonously unusable if it's not stewarded properly. It's accepted among most reasonable/sensible people that oil, especially, will run out, and sooner than anyone would like. Daybreakers takes that sense of overconsumption dread and applies it to a world run, and mostly populated, by vampires. It freshens up a largely corpsified genre in doing so, but casts its initial goal aside in favor of pursuing a more well-trodden action movie course in the end. In doing so, Daybreakers becomes the Equilibrium of vampire movies: smart, but not smart enough to save itself from itself.
Daybreakers is strongest at its beginning, as the Spierig brothers unfold their metaphor in stages. As vampires now dominate the globe, blood has become the most precious commodity imaginable (petroleum, for which blood is the film's most obvious stand-in, never gets mentioned, except in a throwaway line about electric cars). A greater number of vampires results in a lesser number of humans, thinning the herd as the predators' numbers increase. Eventually, the vampires are going to run out of food.
Bromley Marks, one of the biggest blood banks/suppliers in this vampiric world, makes it their business to integrate blood ever more thoroughly into the vampires' world. Homeless vampires beg for blood on the streets; it even gets added to coffee, for crying out loud. They warehouse humans - much like the robots in The Matrix, only with a lot more frontal nudity and facial masking - to farm them for their blood.
We join the film as the blood crisis is already in progress, though its peak is yet to come. Ethan Hawke plays Edward Dalton, a Bromley Marks hematologist. Dalton's the company's golden boy, tasked with developed an artificial blood substitute to alleviate the crisis. It's the perfect task for him, because as we'll learn over the course of the film, Edward loves those filthy humans. He won't even drink their blood.
He goes so far as to protect a group of fugitive humans from the roving human hunter squads who set out to squeeze every drop of blood left in the world. Edward's brother Frankie (Michael Dorman), actually, is one of the best in the business - he relishes hunting down humans with a special pleasure. Frankie, actually, was the one who turned Edward into a vampire. Edward didn't willingly join the vampires' numbers, which goes a long way towards explaining his sympathy for those still human, and the furor with which he hunts for a substitute.
A side effect of the blood crisis are the vampires called "subsiders," ones who've gone so long without real blood that they've begun feeding on themselves. This self-feeding begins a fast-acting devolution mutation that turns subsiders feral and beastial in terribly short order. They become mindless consumers of any flesh and blood they can find, and the vampires can't kill them fast enough.
The other side of the subsider coin is Willem Dafoe's character Elvis - a former vampire who's somehow been able to return to his human state - takes Daybreakers away from the metaphor it'd taken care to construct and sets it on a different course entirely. Elvis has effectively been able to burn his vampirism away in daylight, and when Ethan Hawke tries to do the same thing (and succeeds), the first ray of hope the film has seen shines through. Humanity can be reborn, awash in the wisdom from its dalliance with eternal life and cannibalism, and this time we can make a better go of it than before. While that doesn't satisfy the real world overconsumption parallels the film built in the beginning, but Daybreakers might still have something to say about our behavior as a species, and humanity generally.
Unfortunately, in the grand tradition of films that refuse to stay true to themselves, Daybreakers junks its parallels to the world's problems in favor of extended action scenes. Blood riots consume the nameless city as vampires grab what they can, as fast as they can. The infiltration and violent escape from the Bromley Marks building revels in its explosive, bloody body count, and in the revelation that Edward and Elvis' blood will - miraculously - turn vampires who drink it back into humans. Elvis was a prophet when he first appeared; now he's a bona fide savior (particularly as the first, and likely second and third waves of reverted vampires will almost certainly have to sacrifice themselves to spread the cure globally). Science, make way for religion. And bullets. And lots of blood.
The way Daybreakers chose to end was exciting, sure enough, but in turning away from the hard question it seemed poised to answer in the beginning, in favor of bullets, gore, and an "off into the sunrise" ending, it left me feeling less hopeful than when the film began. If a simple movie positioning itself to answer one of the big questions of our time gives up halfway through, what hope do we have in reality?