XCOM: Enemy Unknown is about assembling an elite squad of exterminators to bloody the nose of an alien invasion, but that's not what it feels like. It feels like tip-toeing upstairs at midnight, kitchen knife in hand, to find out what that rattling noise was in the attic. Most strategy games place too much information at your disposal to inspire dread - you'll always where the enemy is and, more importantly, what the enemy is.
But exploring a map in XCOM can be as harrowing as heading to Silent Hill for the weekend. Anything could be lurking outside the field of view - spider-crabs who breed by stuffing their eggs into people, alligators holding plasma bazookas, flying saucers that unfold into bristling origami sculptures of doom. You just don't know.
The unease is heightened by the awareness that making a wrong move could have even more terrible repercussions down the line, decimating your force ahead of some critical encounter. Enemy Unknown is split between the testing rhythms of turn-based battle, waged on some of the most cunning, replay-friendly maps in the business, and an over-arching strategic narrative where you expand your underground base (displayed in pleasing cross-section), research upgrades from battlefield salvage and cosy up to the embattled nations funding the whole endeavour.
Time doesn't proceed till you scan for alien activity, so there's leisure to pick over the minutiae of your base, zooming to inspect an industrious cluster of eggheads or to watch a man eating dinner in the barracks. Once you do spin the big blue hologlobe, however, there's no telling what the game might throw at you.
You may be called on to quash a spate of abductions, or fish a VIP out of a tight spot. A UFO might take a pop at one of your satellites, threatening to plunge an entire continent into darkness unless you scramble an interceptor to splash it. You don't have to respond to each event, and when the sickbays are full, it may be wiser to hold off. But doing so will cost you political capital, which translates to a smaller payout each month.
Worst of all are the Terror Missions, genocidal pogroms where the idea is to save as many civilians as you can. Fail to answer the call of duty, or allow too many innocents to perish, and the country affected will pull support in protest. Lose eight sponsors, and it's game over.
Nowhere is XCOM's cocktail of short and long-term risk and reward more potent than in soldier customisation. A veteran trooper is worth his weight in gold, whether he's armed with a kevlar vest and grenades or an Archangel flight suit and a plasma rifle.
Each class offers a dozen different upgrades, some of them mutually exclusive, which add up to hundreds of unique, powerful possibilities. You'll unlock these abilities faster if you field the same four to six troopers each time, but fail to train up a few substitutes and a single disastrous mission could cost you the whole war.
Battle itself couldn't be further from the bland, archers-behind-spearmen routines of many Japanese turn-based strategy games, and is let down only by presentational glitches like units occasionally shooting through objects. Range and angle heavily affect accuracy, so victory is about luring enemies into a killzone without exposing your squad in the process.
The AI is sharp enough, but you'll find it harder to fox fellow Earthlings in multiplayer - a pick-and-mix affair where each player has a certain number of points to allocate on units, abilities and gear from both the alien and human line-ups. This feature feels a little perfunctory, but XCOM doesn't really need an inventive mode selection to entertain. Thanks to the sheer number of variables in play, the smallest of dust-ups has the potential to erupt into a two-hour disaster movie beyond Michael Bay's wildest nightmares.