A secret war between two clans of immortals has been raging all around us for centuries. You think we would have figured something was up from the epic gun battles or the digitally enhanced werewolves loping through the shadows. This battle is the subject of “Underworld,” currently tops at the box office. Forget what you know about battling immortals (especially from the “Highlander” movies ) that won’t help you here at all.

“Underworld” reinvents vampires and werewolves, thrusting them into the 21st century with mixed results. While the costumes and sets are incredible, certain things are jarring, like vampires using laptops or werewolves clutching automatic weapons in their claws. Anyone who’s ever argued with a friend about whether werewolves or vampires would win in a fight should definitely check this out. Not for a definitive answer, but just to see what happens when the claws come out. Or in this case, the guns.

“Underworld” is the story of vampire “death dealer” Selene (Kate Beckinsale — think Goth Spice) caught between her disillusionment with the progress of the war and her growing fascination with confused human (or is he?) Michael Corvin (a well-muscled Scott Speedman). A subplot deals with the potential intermixing of werewolves and vampires (anyone who’s ever argued with their friends about this should seek counseling) and the quest for genetic supremacy. For the most part it’s an action movie, lightly treading the borders of horror and fantasy.

Central to the movie’s plot are a number twists and reversals. Our task is to figure out who are the good guys and who are the bad guys. Unfortunately, the characters lacked sufficient development for me to become invested in them, making it hard to care about even the most dramatic of revelations.

Selene’s thirst for righteous vengeance is as great as her thirst for blood, but despite her noble motives it is difficult to muster up any real compassion for her. She often comes off as frigid — after all she is dead. Michael, her love interest, spends most of the movie trying to figure out what’s going on, a plight we can easily identify with. Although both Vampires and Lycans are hunting him, his character is so underwritten they might as well be fighting over meat.

Beckinsale and Speedman’s screen romance never progresses past mutual intrigue. Their most tender lip lock is when he gives her mouth to mouth resuscitation, a disappointment to anyone familiar with the rich sexuality of vampire lore. The other characters are even more marginal, barely registering, with the exception of Michael Sheen playing a sympathetic werewolf and Sophia Myles as a manipulative vampiress.

“Underworld” is written by a stuntman and the guy who plays the enormous werewolf, among others, so don’t expect too much from the script. In addition to ominous voice-over narration and flashback sequences, characters frequently stop the action to explain things to each other and presumably to us. This creates serious problems with pacing, especially because the movie switches so quickly between these tedious expositions and chaotic fight scenes. The unintentionally comic dialogue prominently features lines like “Leave us,” “Ah, yes, we have much to discuss,” and “I’m not doing this for you. I’m doing it for me.”

Part of the problem is simply that the bar has been raised. After experiencing the snappy writing of “X-Men,” the carefully constructed universe of “The Matrix” and the human drama of “The Crow,” audiences have every reason to expect a lot from “Underworld.”

Its failure to deliver is a disappointment, but the movie is eager to please and so some of these things can be overlooked. Underworld is best when it shows instead of tells. Its stylish and seductive visuals are striking, particularly its battle scenes and the lingering shots of Beckinsale’s pale face and leather-clad body. Director Len Wiseman, soon to be Mr. Kate Beckinsale, relies heavily on his experience as a music video director to create a highly stylized film. The sets, costumes and special effects are incredible. An eerie blue glow infuses the shadowy landscape of decrepit old buildings and murky underground tunnels. Death dealers strut around catwalk-style in leather and vinyl. Even their guns are sleek and sexy. Other vampires lounge around the mansion (part castle and part high-tech surveillance facility) in velvet, drinking blood out of crystal goblets. In light of this opulence, you can’t help feeling sorry for the Lycans who live underground and dress like homeless people. (Supposedly, their derelict appearance helps them go unnoticed.) To make up for it, their digitally enhanced wolf form is the stuff of hairy, sinewy nightmares.

“Underworld’s” other triumph is its fight scenes. Successfully employing the aesthetic of video games and comics, it creates tension as the camera skirts the darkness, trying to follow indistinct figures and the echoes of gunfire. The fighting can get overwhelming, but it is as exhilarating as it is chaotic. And thanks to Dolby digital sound and high picture quality, you too can feel like you’re being chased and shot at by vampires and werewolves.

Culminating in the battle to end all battles, “Underworld” generously provides an open ending fueling speculation about “Underworld II.” Hopefully, if there is a next time, the filmmakers will figure out a better way to mobilize their strengths and minimize their weaknesses — perhaps a remake of “Thriller.” Despite all the criticism, I really enjoyed this film and hope that all parties involved got to keep their costumes. Like its characters, “Underworld” reveals itself as a sinister beast, but asks for no redemption, merely suspension of disbelief.