Magnificent fun.

You start off with a bunch of rookies, and depending on the difficulty level, you either build up slowly and save the world, or it's a frenzied juggling of units, supplications to the divine that the aliens do not attack you while your injured troopers are recovering.
Customization of your troops' appearence, names and callsigns really help make you care about X-Com troopers. The only downside is you can't name your Super Heavy Infantry Vehicles ( SHIVs), basically automated killbots on your side.

WHY ARE YOU STILL READING. GO BUY IT NOW.
WITH DISCOUNT IT'S EVEN MORE WORTHY.

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