Underworld is not a vampire movie or a werewolf movie. It is rather, a hyper-stylized sci-fi/action movie that just happens to have vampires and werewolves in it. Horror freaks step off. This is a good movie, but it isn't your movie.
Underworld exists in a washed out reality, where vampires and werewolves roam the earth, just under mankind's radar. Once allies, for centuries now they've waged a secret war on one another, a war the vampires have all but won. The film opens with a dark and beautiful shot of Selene (Kate Beckinsale, looking as spectacularly sexy as anyone could ever possibly look) perched like an eagle atop a building on a rainy city night. She's hunting werewolves (they call them lykens or something but who cares about that) and she's good at her job. She leaps from the building to land on the street, several hundred feet below... and hits hard. That's one of many little bits of coolness that Director Len Wisemen has worked into his film. Vampires don't fly, but they can certainly jump. But when they land, it isn't some weird bit of floaty acrobatics. She lands with an UMPF and flexes her knees. People, even super-powered people, have WEIGHT in this movie, something that other films don't always seem to get right.
After an initial and entertaining battle in the subway system, Selene uncovers a new werewolf plot to destroy the vampire nation. It's complicated and not really worth sorting out. The upshot is they need blood from a guy named Michael (Scott Speedman) to make them all-powerful. Selene finds him, and spends the rest of the movie protecting him, both from the werewolves and her own vampire coven.
What you won't see in this movie is a bunch of wooden stakes being pounded into hearts or garlic being waved in a pointy toothed person's face. Underworld takes place in a modern age, thus it only makes sense that combatants are armed with modern weapons. I know the Highlander universe has a lot of fun with swords, but couldn't you blow heads off better with a bazooka? Vampires have semiautomatics loaded with silver bullets for taking down their werewolf foes. The wolves have had to get a bit more creative and use a weird glowing bullet thing that transfers ultraviolet radiation (sunlight) into the body of their vampire victim. If you've some vampire purist, maybe you won't like that, but it makes enough sense within the realm of established vampire mythology to work for this movie... which I've already pointed out is an action movie first and a vamp movie second.
Underworld's biggest strength is obviously style, which leaks out of every frame and into your eyes. Director Len Wiseman uses a very sharp sucked-dry look, which brings a stark unreality to his movie. He also doesn't mess around with keeping things linear... though the film takes place over several days, it exists in an almost perpetual nighttime of lightning and rain and dark dark shadow. OK, maybe it is a bit curious that there's no sun, but don't worry about it. I didn't mind. Yes, his characters wear a lot of leather and long black coats. No this isn't a Matrix rip off. Any comparison ends with their clothes. Underworld is clearly inspired by gothic influences, but there's no bullet time effects or weird slow motion kung fu. Wiseman has his own ideas and his own sensibility.
As both sides, vampire and werewolf collide, Underworld keeps your interest with a variety of great action sequences and pseudo-romance between Selene and Michael. Speedman is a little wooden, but isn't given much opportunity to really open his mouth. That hurts the film in the final chapter though, when he goes through an almost "Hulk-like" transformation. Personally, I would have made him look a little less green. However, at least Beckinsale knows her business and plays her character to great effect as a grim and hardened warrior. She's never portrayed in a sexual way, despite being a female lead wearing extremely tight clothes.
Some of the quieter moments of the film dip into the politics of Selene's vampire coven. There, she's at odds with Kraven, a sniveling vampire bureaucrat whose been left in charge while the real vampire leaders sleep off an 18th century hangover. Kraven (Shane Brolly) could have been an interesting character... if the guy playing him knew how to do more than scream at his fellow cast members, spraying them with a seemingly never ending fountain of spittle. Beckinsale does her part, but some of the film's other minor character's come off as B movie rejects.
That isn't the case with Underworld's heavies, who display ferocity through physicality, rather than whiny boy spitting. The werewolf transformations are well done and a lot of fun, particularly the first time you see them. Michael Sheen has a wonderful subplot as the werewolf leader, including a flashback love story that easily outstrips the somewhat flat emotional tension between Beckinsale and Speedman. His vampire counter-part, the vampire mega-leader Viktor (Bill Nighy), plays a good balance to him, keeping things twisted and disturbed. Wisemen uses some great cgi effects to make Viktor move in an almost normal, but not quite human fashion. Another one of those subtle bits of coolness I mentioned earlier.
Underworld is exciting, engaging, and not entirely perfect. The best moments come from stunning cinematography and set design. Wiseman's look is so good that even were the rest of the film a wash, I'd still recommend it. Wisemen knows what he's doing, and what's more does it on a comparatively small budget. Maybe the rest, including some fairly mundane fights in the sewers isn't exactly groundbreaking. Still, if you're just looking for some fun in a dark, disturbed world of gothic, heavy metal loving gods, Underworld delivers.