The Ogre Battle saga, but probably if they released some more games to help develop the story, constructs and classes to a point where they're more stable.
I'm also thinking it'd be best being some kind of 'you control a whole team' thing like the games themselves, not the one-toon-timesink that most MMOs do. It's not that the single-person formula is bad or anything, I just think it'd be impossible to balance all the classes for PvP like WoW and other games try to do, as well as the fact that it might work more easily if you're using whole teams and such, the way the games of the saga do.
You could raid things all on your own, or toss one/a few of your units in with some pals and do some map-scrolling multiplayer stuff, or something.