That's weird. I think the SimCity4 is quite simple and I's say there are too few factors to manage. But even now, with dozens of customs lots it's visually astonishing despite of course of its artificiality.
What I look in city simulator would be richness of modded SC4, more flexible environment allowing creating of the 'real' cities, real and accurate height maps from all around the world, combined with real troubles and decision making of city planner and the mayor. And this whole stuff placed in customized environment, "country" of some kind, with certain fiscal and international policies.
Maybe I'm exagreggating the meaning of 'real'. Some giant Death Droid invasion would be cool also:)
