MMOs really don't appeal to me. The hack and slash only keeps me satisfied for maybe 20 hours of gameplay.
I enjoyed
A tale in the Desert for a while, but it suffers from what I call "anti-entropy", by which I mean there aren't enough destructive forces to balance the constructive forces.
Ideally I'd like an MMO where players are dropped in a virgin wilderness and they just live a life. Cutting down trees, hunting prey, etc. From that an emergent civilization, perhaps currency and laws, might develop. And all player actions (such as cutting down a tree) have long term repercusions (tree doesn't respawn somewhere else, though an existing seed might grow into a new tree).
Which I would like to eventually work on to create a simple demo for something like that, but I don't know enough to get something going satisfactorally.