The demo runs just fine on my rig (2 ghz processor, 512 mb ram, 128 mb ATI Radeon 9600, etc).
As for gameplay, I haven't had enough time to tinker around with it but there seems to be a fairly large amount of changes to the game, some of which are cool (the ability to hire indian allies and control trade routes) and some which are retarted (like the 'home city' concept and the fact that you have cards that you can play throughout the game to gain special power-ups).
I do like the graphics, though, and the setting is cool. Ultimately, though, this is just another AOE game. Which means I'll be waiting on Civ IV later this fall.