First is, of course, Internet multiplay. Multiplayer is where the fun begins. No computer AI can match the perfidy and duplicity of humans. He was a constant distraction and I have the sneaking suspicion that, despite his poor position in the game when we all threw in the towel, he had as much fun as anyone did. No AI will do irrational things just to tick you off, nor can an AI be reasoned with, intimidated, bluffed, or cajoled.
Humans make deals that are many degrees of subtlety beyond anything on silicon.
Multiplayer games are available through the MS Zone. So, unless you have some bandwidth, when you start it up, have something else to do for a while. Typically people don't intend to spend 6 hours online playing a single game, so most multi games will have a multiplier to production, unit speed, or both. Chatting is accomplished through a moderately functional popup window, with the ability to selectively mute individuals. I think I don't like that, despite the in-game logic that argues in its favor.