In other words: Did you ever borrowed or rented a game that you wanted to complete which then you never did?
Last year I borrowed Tales of Vesperia from a friend and I only played half of it, now he doesn't have it and I can't find a copy anywhere, since to this day I've seen friends on Xbox Live playing the game, now I feel bad that I'd never completed it... :(
So what's your game that you've never done with but you wanted to?