I have a bad habit of doing this, but usually I get around 50% then maybe move on. I tell myself I'm saving them for a rainy day or slow parts of the year. But the more I do this the more I realize I should just finish while I'm into the game, sucks trying to pick up a game after months of not playing. I did this with MGS4 and now I get owned because I saved at a hard part.
Those are all awesome (Bioshock 2 maybe not so much) so pick one and give 'em some lovin!
I hope it is persistent instead of the usual round based zombie waves. If I have to start from the beginning each time I fire it up then I'll pass, but I would love a 1-2 player offline MMO for now if that is what they are working towards.