I would have to say Dawn of War. I have installed and uninstalled that game more times than I can count. I really really like that game, but yet I cannot seem to finish the campaign. I usually will get to mission 9 or 10 / out of 11 , before I mysteriously quit...and I can't pinpoint why. It's my favorite RTS of all time right next to freaking Battle for Middle Earth II. Considering I luckily still have my Dawn of War installed, I think I might try to finish the campaign on Christmas Eve...I am not holding my breath though. xD