One word, Disgaea.

Disgaea would make the ULTIMAGE MMO.

Why? Think about it:
You get to be an overlord or a demon working upwards to be an overlord
You'll get to conquer other Netherworlds
You can be an Angel from Celestia trying to destroy the netherworlds
You can run into other Overlords (i.e. Alexander, Pram, Laharl, Zetta)
BE A PRINNY! xD
DISGAEA NEEDS A MMO!! xD