1 game? really? But... damn it. Well, it would either be Spyro 2: Gateway to Glimmar or Ratchet & Clank 2: Locked and Loaded. Probably the former; the latter was more of my tween years.
Edit: Actually no, Sonic Adventure 2 Battle. The game that got me my first real friend, whom is still my closest friend today.
Edit: Actually no, Sonic Adventure 2 Battle. The game that got me my first real friend, whom is still my closest friend today.