
This was realeased yesterday and I just picked up a copy today. I am going to while away the afternoon playing around with it.
It looks like a really worthwhile expansion, advanced start for mp, all the Warlords additions (traits, wonders etc.), new techs, wonders, proper espionage now and way earlier, new units, improved air combat, Corporations (function a bit like religions), interesting tweaks to siege combat, some good scenarios, new promotions, leaders and best of all, tactical nukes.
Expect a new pbem game as soon as there's a critical mass of players with this...
Its available to buy from Steam & Direct2drive (Gamespy) next Monday. The Steam version works with box versions of Civ 4, I believe.