elder scrolls: oblivion, completed main quest, dark brotherhood and arena and maybe one or two other sidequests, then it started to bore me, there was a truckload of sidequests available, but none were of my interest.)
thief: deadly shadows, didn't bother doing the last couple of levels, i always end up sneaking up and then getting a truckload of people behind me all the sudden, then i usually die. then i un-installed it.
unreal tournament 2004 single-player, couldn't beat the last mission. god-mode bots are almost insta-kills everytime they see you. thank god there was still multiplayer which kicked ass.
half-life 2: episode one, in the mission where your train stops at some zombie-cluttered fuck-hell you rely on your flashlight, my first though was that i had to strafe thru the entire map as fast as possible whilst collecting energy, every time my flashlight ran out and i was in total darkness, later i found out (when i un-installed the game) the flashlight re-energizes itself when you turn it off. never bothered to install the game after that.