X-COM 2: Terror From The Deep was actually my first exposure to the X-COM universe, and turn-based tactical games as a whole. Given how absurdly difficult it was to me, I’m surprised I maintained enough enthusiasm to investigate the rest of the series. But, boy, I’m glad I did! Finishing the original X-COM is one of my proudest gaming accomplishments.
X-COM 2 was also my first introduction to hex-editing. But- shhh… don’t tell anyone.