Despite their age, it's amazing how well the old citybuilders hold up. Even if you can't bring yourself to delve into the, uh, 2D-ness of the very old titles, there's always Caesar 4. However, if you love isometric sprite-life of Impressions' early games, then GOG has a nice surprise for you.
GOG already had a healthy selection of class citybuilders, including Pharaoh, Zeus and Caesar 3, but if these failed to be retro enough for your tastes, its hard to go further back in time than the original Caesar.
Understandably, Caesar may be a little too dusty, in which case the second game would be the tastier treat. Of course, when it comes to the cream of the crop there's always Emperor: Rise of the Middle Kingdom, arguably Impressions' finest effort in the genre it helped create.
All three titles are $7.99 and you can grab a bundle including several other titles from Impressions Games for $46.