NieR: Automata

Yoko Taro made a game about androids fighting robots and somehow turned it into the most profound meditation on existentialism since Sartre. The trick is that the "real" story doesn't start until your second playthrough, and the true ending requires you to sacrifice your save file to help a stranger. Over 6 million copies sold because word-of-mouth kept insisting: "just trust me, keep playing." They were right.