Whether we mean to or not, we get pretty invested in the online worlds we inhabit. It's a natural step to go from a single-player setting that's already gotten our emotional investment to a larger one (as proven by, oh, some game or another
), but oddly the reverse happens far less often. We only occasionally see a game that takes the setting of an MMO and uses it as the basis for one person's adventure. This despite the fact that we're usually more attached to our characters than we are in a single-player game, since our avatars in an MMO are defined entirely by us.
Of course, part of this is the narrowing of scope, and part of it is the difficulty of marketing to people that they can take a break from their characters online to play the exact same character offline. But for the times when you don't want to log in and deal with assembling a group or competition for farming or any of the slings and arrows of playing online, it could be a nice diversion. What do you think? Would you like to have a single-player game based off of your MMO of choice, or would you rather that the online games you enjoy not creep into your single-player time?