Kiutu said:
I played Morrowind for hundreds of hours and I never came close to beating the game (or running out of content to explore).
I'd say the game I've "completed the most" probably is Deus Ex with three full play-throughs. It wasn't exactly a short game either so it takes some time to finish. I'm actually a sucker for that specific hybrid of game, and Deus Ex, System Shock 2 and Vampire: The Masquerade all rank pretty highly with me.
If it becomes a question of "what game have I played the most" the answer is almost certainly Mechwarrior 4. While I may have played Tribes and Team Fortress (Quake) obsessively, Mechwarrior 4 was a fairly long term commitment. I would run out of content and had reached the limit of what I believed could be accomplished in the mechlab, and just then a new expansion would drop that would change the face of combat in the game. If you count the initial release, it's expansion (Black Knight), the stand-alone expansion (Mercenaries) and the pair of mech-packs, you'll find that I played the game regularly for more than two years.