XCOM: Enemy Unknown is both the best and worst kind of stressful. Building up your base, researching tech, and then sending your soldiers out where they might actually die? Brutal but awesome. The tactical combat is super tense, and the stakes get crazy high. Might not be for everyone – one bad move can screw you over, and the permadeath is rough. But if you like turn-based strategy and don't mind the frustration, XCOM will suck you in like crazy.