To sum this game up, I can offer a few suggestions. Give Diaspora time, it grows on you and what appears simple has amazing depth. Plus, Phil sums it up rather well. There are many things that set this apart, but I think the most important would be its sense of community. With chat facilities everywhere you go, the ability to create your own guilds, the bulletin boards and the full interaction with the other players, it adds so much to the game.
People can just stop into the game for a chat or to meet friends as well as to play the game.
It is that level of communication that brings the game alive. People themselves are a lot more interesting and unpredictable than any preprogrammed characters. This really gives the players the chance to develop roles and play out their characters.