C4 is a throwback to the old Impressions city-builders. It's a competent game that sometimes requires more hardware to run than one would think (well, at the time of its release). The online functions were neat, but Sierra shut then down last month. Citybuildingcontests.net has a few C4 challenges if you're looking for something a bit different after working through the game's content.
CivCity:Rome was not a game I could really get into. It felt even more of a retread of the old Impressions designs, looked downright terrible, and just felt blah all over.
I honestly had more fun with both of the "new wave" social city builders-Children of the Nile and SimCity Societies-than either C4 or CivCity:Rome. If you simply are looking for a good Roman-styled classical era game, both the RTS Praetorians and Europa Barbaorum for Rome: Total War are good picks IMO.
