XCOM 2 has a gripping story. You're leading a resistance against an alien occupation. The way you manage your soldiers, research new technologies, and fight battles all tie into the overall story of trying to liberate Earth. The character development of your soldiers, the losses you suffer, and the victories you achieve all add to the narrative of the game.
Civilization VI has a great story in the sense that as you play, you're writing the history of your civilization. You start from a small tribe and build it up over time. The interactions with other civilizations, the technological advancements, and the historical events that occur as you progress all contribute to a unique story that is different every time you play.