Video-game aliens have gotten bigger, uglier and meaner over the years. Think of the Covenant warriors in "Halo" or the Locust Horde in "Gears of War": huge, dumb, slobbering brutes who can soak up plenty of bullets before they pounce on you and crush your skull.
The extraterrestrial invaders in "XCOM: Enemy Unknown" (2K Games, for the Xbox 360, PlayStation 3, $59.99; PC, $49.99) aren't exactly benevolent - they have come to Earth to enslave humanity - but their advantage is more technological than physical. Indeed, the first aliens you encounter, the Sectoids, are so scrawny they look like a stiff breeze could snap them. But their laser guns can disintegrate human flesh, and some of them can take over helpless Earthling minds.
"XCOM" (as in "extraterrestrial combat") is a throwback to the golden age of science fiction, when bug-eyed monsters stalked the pages of pulp magazines. The story is nothing new - a relative handful of stalwart men and women make a last stand against overwhelming odds - but the developers at Firaxis Games know how corny it is and have some fun with the melodrama.
Take the Thin Men, aliens who are bioengineered to look like humans, only to be given away by their discolored flesh and reptilian eyes. Or the insectoid Chrysalids, who lay eggs in their human victims, who then turn into zombies until they explode and give birth to new monsters.
Fighting for the good guys, you have a couple of gleefully deranged scientists who seem more obsessed with studying alien tech than with saving the planet. And you have the shadowy Council, a global consortium that keeps pushing you to fight while barely providing the resources you need.
During field engagements you have four kinds of troopers: Assault, who are skilled in close combat; Heavy, who can lug around machine guns and rocket launchers; Support, who make good medics; and Snipers, who are deadly at long distances. The more missions they survive, the more skills your troops earn, and you'll need a good mix to defeat the increasingly powerful invaders.
This isn't the kind of combat that "Halo" fans are accustomed to. Instead, "XCOM" revives a genre that has rarely been seen on game consoles: turn-based strategy. Essentially, you take a turn moving your troops around and attacking the aliens; then the game's artificial intelligence takes over and strikes back.
As each mission begins, you can't see the enemy. Rushing headlong into the fog of war is a good way to find your squad outmanned and outgunned; it's wiser to take things slowly and try to pick off the invaders a few at a time. It's like chess with plasma rifles, and it's a refreshing break from the usual run-and-gun mayhem of video-game combat.
Firaxis is best-known for its landmark strategy series "Civilization," and players who enjoyed conquering the world in those games will have just as much fun saving the world in "XCOM." On the other hand, those who have been intimidated by "Civilization" - or just don't have the time for its epic, dayslong matches - will find "XCOM," whose missions rarely last longer than an hour, easier to get into.
The original "X-COM" (with a hyphen) came out nearly 20 years ago and is still regarded as one of the greatest PC games ever. But for all its retro trappings, the new "XCOM" feels entirely fresh. There's nothing else like it on consoles. Three and a half stars out of four.