My old buddy from the past is called Deus Ex. You might remember that game. It came out in 2000 and it's a first person stealth-RPG with shooter elements. The most striking thing about it is that you have the freedom to explore and gather information to approach your objectives, discovering many secrets along the way.
Deus Ex takes place in a dystopian future in a world that draws heavily upon popular real world conspiracy theories for many of its plot elements. You play as JC Denton, a nanotechnologically-augmented UNATCO agent. As you are making progress in the game, the story unfolds itself into a spiraling twist of revelations and it all comes together in a beautiful crescendo of epic proportions.
I tend to replay Deus Ex every year, and each time I discover new things on those playthroughs. Even thought the game is still perfectly playable as of today, I still wish for a HD remake of this game. Deus Ex with todays graphics? Oh, hell yeah.
So, what game from the past holds you dear?