Maybe a subject for another thread? Although I think you’d have to ask along with it “why did it change your life”, its not always so straightforward with game titles to get a feel for what the game is about.
I will kick things off…
Panzer General (1994): I spent way too much time playing this, marshalling little WW2 armies in the desert near Tobruk and in the European theatre. It led to a fascination that lasted decades about generalship and armies and game systems.
Ultima Underworld 1 and 2 (1992-1993): The first fully 3D games that I played, way ahead of their time. In the end I ended up programming 3D game engines professionally, and made a career out of it.
World of Warcraft (2005): The first massively multiplayer online game I played, I got quite severely addicted to this, it was not healthy the amount of time I played this in its Vanilla incarnation. Led to a fascination with game analysis.