XCOM: Enemy Within is a turn-based strategy game that follows the story of Earth's resistance against an alien invasion. The player takes on the role of a commander, leading a team of soldiers through various missions to fight off the enemy.
The gameplay involves tactical planning and execution, with the player needing to place their soldiers in positions to take down the enemy while minimizing losses. As the game progresses, new enemies are introduced, requiring the player to adapt their strategy to succeed.