I think I would have to say KOTOR I or II. TF2 has easily been the game I've spent most time with though
FF7. Chocobo wars....running around the "tactical map". So inavative for its time. The adventure, the replayabilty, the characters. No other game hooks me in like this one dies every 2-3 years. I have to pull it out again for another play thru. And the lylat wars comment....................oh the memorys and the frustration of playing it when ur 64 controller joystick dead spot was almost the full range of motion. Great fun