The Legend of Zelda
If you didn't see this coming, you don't know me very well. I played the original Legend of Zelda for the first time in 2007, near the game's 20th anniversary. Like any decent, God-fearing individual, I sat down, took some paper, and drew a grid on it. As I moved through the game I made a map, noting where one could move between screens (so I could plan a path, you see), where items and heart pieces were, directions for how to get through the Lost Woods, all of that. I fought through hordes of enemies the likes of which would make most adventurers crap their pants, collected magic items to make myself stronger, and very slowly made the land of Hyrule into my own realm.
This game is perfect, one of only three games that I would readily give that distinction to. Its design is flawless and fun from end to end, the music never grates in spite of looping so often, and when you finally triumph over evil the feeling of reward is far greater than a video of the ending might lead you to believe.
This game is the progenitor of what may well be the greatest series ever made. More than that, it's a game whose greatness communicates itself more than two decades after its release. I am singular, living proof of that. Among the gloried host of its own series, this game stands proud, unassailable, and will never be too old to be awesome.