XCOM: Enemy Unknown

Firaxis's 2012 reboot took a 1994 strategy game with a devoted following and made it playable without losing its cruelty. Two layers run in parallel: a base-building and research campaign where you decide which panicking country to defend and which to lose, and turn-based squad tactics where six soldiers with two actions each fight aliens in destructible cover. The soldiers are the hook. They are randomly generated, promoted into specialisations, renamed by you, and permanently dead when they die, which converts a percentage-chance miss into something people still complain about a decade later. Overwatch, flanking and the height advantage make positioning matter more than gear, and the fog of war means an unscouted room is a real risk. The Enemy Within expansion added gene modding, mechanised suits and a human enemy faction. Its success is the reason turn-based tactics stopped being a dead commercial genre, and the reason XCOM 2 was allowed to be considerably harder.