You're HAZMAT specialist Ethan Cole, called in to run clean-up when something goes terribly wrong at a top-secret government testing facility. Operating alongside fellow commandos, you must venture deep into the base. But before you even enter the complex, it's apparent something's amiss. For starters, after wreaking considerable havoc, a rogue soldier who's escaped from the installation literally dissolves when shot. Then there's another more disturbing fact that quickly dawns on you: everyone you meet not only sports a distinctive personality, but looks, talks, and behaves as a real human would.

Thus the game's greatest strength is quickly revealed -- it's immersive as hell. Wandering burnt-out corridors, decrepit maintenance areas, and immense silos scintillated with fluorescent light, you'll feel the tension mounting. So when humanoid horrors ravaged by a mutagenic virus come screaming from the shadows, it's that much more unnerving. Along similar lines, watching teammates (whom you'll become personally acquainted with) bite it from inches away is shockingly upsetting. Chalk it up to "X Factor;" the game possesses an intangible quality that sucks you in and grabs you by the seat of your pants.

Most of the tale revolves around riveting shootouts with four-eyed wall-crawling freaks, crab-like insects and goo-filled soldiers. Created by Hollywood special effects legend Stan Winston, creatures are prone to springing from ledges, leaping through windows, and otherwise scaring the crap out of you. Worse, monsters take several shots to drop and are able to seek cover, flank you, and even counter your tactical attacks with its own. Not all adversaries rely on tooth or claw either; a bald, shriveled beast that was once a man may end up peppering you with machine gun fire.

It also helps that most encounters, although scripted, deliver tangible impact. At one point, you're pinned down behind a blockade with a handful of allies when dozens of enemies charge. Comrades are picking off distant adversaries, grappling with closely situated foes, and screaming with bloodlust. Meanwhile, troopers in turrets shriek out warnings while using explosive shells to blow baddies away with screen- and speaker-rattling effect. Amidst the chaos, you're just one of many inhabitants of a fully realized virtual world. Never mind that the path through the game is largely linear and framerate slowdown proves common. You'll always feel as if you're right there on the front lines.