I have to say that the private server makes this game for me. It's way more fun to play survival co-op in a persistant world with other people i know.
It's really cool to build our own little community and hang out! Up until now I had owned a copy of mine craft, but never really got into it, private multiplayer makes it!
If anyone else here is on the fence, jump on in! You can come ride my recently opened mine railroad!
