Been reading over all the stuff from Sulla and others with all the new info, and a few things caught my eye that sound really cool:

1. "yes, you can play a team game with the AI if you want to even in Single-Player...." This sounds like it might be fun. Apparently you could start with like 8 civs, have 3 of the AI on your side, and go team against the 4 on the other side. I can see some possibilities here for long nights.

2. An option for "no technology trading". How many times in CIV3 have the AI civs ganged up on you by trading all the tech around while you had nothing to trade for it? Well now you can stop that - of course I assume it also means that YOU can't trade....

3. The "quality" of units seems to be much more important than in CIV3. Especially since you can now get some really good promotions for them. No more of that stack of death with 80 tanks and 20 Mech Inf. - YAY

Lots of other things new, obviously, these are just a few of the big changes I noticed that will basically make this a whole new game.