13. XCOM 2
XCOM was always a hard game, but XCOM 2 made that part of the fiction rather than just the mechanics. You're no longer part of an organization dedicated to stopping an alien invasion with the backing of world governments, now you're playing as the ragtag underdogs fighting aliens who have already taken over the world. Every advantage has to be scrounged for, and even your base is made from a stolen spaceship. XCOM 2 is also faster-paced, thanks to that zippy spaceship and time limits on the battles (still turn-based, of course). It remains a game of weighing percentages before risking a move out of cover, but its new sense of speed makes it a tense, and even more exciting experience.