Sega's "Aliens vs. Predator" (Xbox 360; rated M) has taken a lot of critical heat since its release, and for good reason - it's not a perfect game by any means. Its campaigns are extremely short (even taking into consideration that there are three of them), the controls are not always intuitive and multiplayer is largely broken.
Still, there's a reason that these two breeds of alien life have lasted in the worlds of comics, games and film long past the movies that originally made them famous. H.R. Giger's Aliens are manifestations of our worst fears - the dark, bugs, snakes, acid - all rolled into fast-moving, terrifying, intelligent beings. Alternately, there's the Predator, whose form makes it just human enough to be identifiable and whose code of honor disguises its own many brutal ways of killing whatever enemy form it encounters.
Going toe-to-toe with either of these species is a game idea so appealing that to botch it is almost impossible. Actually inhabiting the bodies of these species is even better.
It's the latter idea that truly works in this game. As an Alien, you move far more quickly than any of the other species, you can scale walls and you can pounce on your prey from long distances. As the Predator, you can shoot a guided blast from long distances, cloak yourself to near-invisibility and, yes, rip the spines out of your prey. (To be sure, there is no doubt about the game's M rating.)
Playing as a human, the game takes on a very standard sort of survival horror type of feel, with lots of dark corridors and sudden scares substituting for imaginative game play.
Multiplayer games feel surprisingly balanced - people may develop favorites, but there's no clear advantage to being any of the three species. Unfortunately, actually getting into a multiplayer game can take ages, and there is an awfully high occurrence of lag and games dropping.
What a player gets out of "Aliens vs. Predator," then, depends on what that player wants. If you're looking for a good first-person shooter - well, there are plenty of better options, particularly where multiplayer is concerned. If you're simply looking for the thrill of coexisting in a universe with the two species that give the game its name, however, "Aliens vs. Predator" is worth at least a rental.