There are plenty of other MSOs … but the successful ones all have some attributes in common:
–All are based on stats, money, loot, rank, and clans or guilds
–The best extent to which players can communicate with each other is through messages, forums, or chat, all of which don’t occur “in game”
–All require alternative and creative revenue streams, and must be free to play. Methods include microtransactions, merchandising, and donation requests
–Actions or turns are limited so as to reduce server loads and costs. Some regenerate slowly every few minutes, others simple reset every 24 hours
–Must have interesting or popular content, especially if merchandising is a revenue model
–They generally prohibit multiple character creation
-They encourage player-banding by heavily rewarding group associations in order to recruit new players to expand the player base and sustain merchandise sales.
This last point is ironic, since these are essentially single player games, but it forges communities based around the culture of the game. In the case of Mafia Wars, that culture is Facebook, which partially explains why player interaction is limited.