It ran well on my machine; in fact when I was playing it my weekly virus scan started and barely slowed the game down at all.

for a point of reference my specs are

Dell P4, 3.00 GHz, 1024 MB RAM, ATI Radeon x800 256MB

I think my new video card is what makes the difference, because there are people with my specs (but different video card) complaining about major lag problems.

I liked it overall, and when I inverted the mouse controls for the camera, I liked it even more.
Some of these have been expressed above, but my main complaints are

The camera often jumps for no apparent reason, especially near the edge of the map.
Often you can click mulitiple times on a button (or to build a building) and nothing happens.
Information is buried - they need hotkeys to each of the advisor screens.
Slow loading to and from advisors-city-empire views.
I wouldn't mind an end of the year report - nothing major, just a popup summary.
The list of buildings to build can really clutter up the screen when you're trying to place a building.