lol at the poll
Spacewar!, and it's not even close.
It basically invented what video games are to this day.
Simulationist. Combat as the central mechanic. Realistic graphics. Collaborative and iterative development. It's even a geek-friendly setting.
Edit: If we are to talk about "commercial" video games, then I dunno, I'd say it's a tie between Zelda and Doom. Zelda because big open-world, adventure game, complex mechanics, memorable music, etc. It's obvious many current video games draw from Zelda. And Doom because it's one giant stepping stone in 3D rendering history.
Edit 2: lol at Goldeneye and MGS.