Manhunt 1 on a machine that could only just run it.
It was fine for most of the game, but in the later levels, when the framerate dropped, I couldn't attack and couldn't go up ramps :/. Also once an event failed to trigger, and there was a line of about 5-6 guys just standing around doing nothing.
Never did complete it, thanks to the stupid glitches that were happening. Most singleplayer games still work at low framerates, as everything just happens slower, but in Manhunt it was actually affecting the AI and the movement.
WoW went through some glitchy stages - falling through the floor, appearing in the wrong location after dying, stuck mobs, unable to leave corpse when dead, unable to res, quest events not triggering/breaking. Having said that, most stuff worked, and most of the time the bugs weren't too annoying.