I'm more into multiplayer games because they show true skill and I have a lot more fun playing with actual people than with npcs. However, I do enjoy single player games. I've been having a lot of fun recently playing the rainbow six vegas campaign and trying to get all the campaign achievements on gears on hardcore and insane.
I just don't think 60$ is worth on a game that won't have much replay value. Even though Bioshock might have a lot of replay value with all the different plasmids that you can use. Gotta get two worlds though, I've been wanting an RPG to play baked since June and didn't want to buy Oblivion because GOTY is coming out next month.

Anyways, with all the reviews that bioshock got, I still might get it on ebay or something.