Fallout: New Vegas
Another game in the Fallout series — the best one. The reason this website looks like a RobCo terminal.
Fallout 3 familiarized me with post-apocalyptic America. New Vegas made that world bigger. There was open desert, bright casino lights, and different groups of people asking you to choose between them.
What you decide actually changes how things turn out. That's why it stuck with me.