Let's see... I get bored really easily so there is quite a list to choose from.
WH40k: Soulstorm - Three missions then I didn't pick it up again in single player for a month. I only started playing again because I would comp stomp with my brother. I still haven't beaten the game with a single faction.
Gears of War - I think I lasted an hour then uninstalled it. Maybe I just expect something different from a PC shooter but after the 20th corridor, the 10th hole in the ground, and clunky controls which made it a minor miracle if I actually got a melee attack in I just stopped.
Bioshock - I made it through the Hospital, I think, but then I was done. I'd probably spend more time on it if my computer was better but after like an hour or two it felt repetitive and I didn't care enough about getting more powers or weapons.
HL2: Ep. 1 - The first time I quit after I hit the surface. About a month or two later I picked it up and lasted to the warehouse then I quit. I have no idea how close I was to the end but I doubt I was far, I just didn't feel like wasting any more of my time on the game.
HL2: Ep. 2 - I installed it, started a game, and then just called it quits and uninstalled it before I got much of anywhere. I couldn't make myself care.
TF2 - I played TFC regularly for a year, on and off for another year and then almost never up until TF2. Fortress Forever kept me interested for a couple weeks then TF2 came out and I think I played for two or three days. Still haven't picked it back up. It just feels 2D compared to TFC, I miss my conc, rocket, and grenade jumping.
