18 cert, 2K Games, Xbox 360 (also PS3, PC) ****

“Two possibilities exist: either we are alone in the universe or we are not. Both are equally terrifying.” Kicking off a game with an Arthur C Clarke quote is a bold move, and it tells you a lot about XCOM: Enemy Unknown. This is an ambitious and sombre affair. Thankfully it also has intelligence, invention and tense, stimulating gameplay that is turn-based and real-time. You lead a military defence against an alien invasion, placing those soldiers on the right part of the battleground and trying to outsmart and outflank those ruthless, slimy aliens. You’re also tasked with researching the invaders, augmenting your team and even choosing which parts of the world to save. The extraterrestrials may look familiar (all bug eyes and giant domes) but their tactics are hard to predict, whether they’re firing lasers, controlling humans from afar or launching serious hardware. The animation is a little perfunctory, but this is a smart, compelling strategy game with real conviction. A gem.