"Daybreakers" opens with a concept so original it's actually exciting, casting an intoxicatingly moody, certainly creepy spell. The opening half-hour is terrific, painting a macabre vision of a near-future both curiously similar and ghoulishly askew from the real world's present. Directing brothers Michael Spierig and Peter Spierig, mounting their first major studio film, have an undeniable eye for the profession and a sharp stylistic sense that calls attention to itself without becoming showy or overly gimmick-laden. Holding less scrutiny is their troubled screenplay, which starts with such promise and underlying subtexts aplenty before going lazy and turning into a standard, even forgettable horror-actioner with little to remember outside of some bloody money shots.

In the year 2019, the majority of the human population have been turned into vampires, the result of a virus begun by a single bat. They live in houses, drive cars, and go to work. They are also always on the hunt for fresh blood, their supply seriously dwindling as mere mortals move toward extinction. Edward Dalton (Ethan Hawke), a vampiric hematologist working at harvesting facility Bromley Marks, still clings to something of a soul as he shows sympathy to the hunted humans. When two of them, Audrey Bennett (Claudia Karvan) and friend Elvis (Willem Dafoe), turn to him for help, Edward agrees. On the other end of the spectrum is Charles Bromley (Sam Neill), a pointy-toothed company bigwig seeking world domination while contending with unturned anti-vampire daughter Alison (Isabel Lucas). When Edward discovers that Elvis was once a vampire himself who somehow changed back into a human, a tinge of hope arises that a cure might not be far behind.

The first scene of "Daybreakers" is striking. A little girl writes a suicide note discussing her eternal childhood and how she "can't take it anymore," walks outside her home at the start of the sun's rising, and waits for death to take her. This is followed by a neat opening titles sequence that dips the viewer into a land gone wrong and yet still basically going on as usual. That the vampire outbreak was started by one bat is probably no mistake—allusions to the swine flu are either wholly intentional or just a really lucky accident—and directors Michael and Peter Spierigs' matter-of-fact depiction of what the planet might be like under these extreme situations is rather haunting in its plausibility. Little details—i.e., blood used as coffee creamer, underground walkways used during the daytime, the nonstop smoking of virtually all the immortals, the Uncle Sam sign hanging in the subway urging everyone to hunt humans—help to bring the setting and circumstances to unsettling life. Meanwhile, a set-piece where Edward and younger cadet brother Frankie (Michael Dorman) are attacked at home by a malnourished vamp creature gone mad is befit with tension and expert make-up effects.

Were the film to continue down this road, expanding the scope of its premise while further exploring the different daily facets of modern vampire living, it might have been a new genre classic. Instead, things expediently bog down via too much leisurely exposition and, as it would have it, too many derivative action scenes. Cars are chased, bodies explode or burn to a crisp, and all the while a personable Ethan Hawke (2005's "Lord of War"), an off-the-wall Willem Dafoe (2009's "Antichrist"), and the rest of their co-stars do what they can as they increasingly blend in with the swarm of chaos around them. When they do sit down for a dialogue exchange, it usually goes on past the point of tolerability and slows the pacing (and plot imagination) to a crawl. The gore-drenched finale, wherein just desserts are handed out and a hope for a brighter tomorrow is eminent, is too little too late, despite some inspired individual shots.

"Daybreakers" isn't exactly good or bad, and that is the problem. Michael and Peter Spierig took the time to concoct an excellent idea—one as timely in its inferences as it is spookily thought-provoking—and then, about one-third of the way through the script, apparently gave up and switched to autopilot. When all is said and done, the film is a discouraging "Underworld"/ "Doomsday"-type affair that has no business becoming as ordinary as it does. The film could have broken the rules and expounded upon its initial ingenuity. It could have been about something. It's not. On the other hand, at least the picture stays true to the basic mythos of bloodsuckers, something the "Twilight" series has defanged and left for dead in recent years. So much for small victories.