They are the pinnacle of Impression Games city building series. The game mechanics are bit more polished. What really sets them apart from the rest of the Impressions Games "oeuvre" though is that they have a charm to them that's missing from the rest of the series. They were a blast to play. If you're looking for something newer, there's Children of the Nile by Tilted Mill, the successors to Impression Games.

Farther afield, you have the likes of Tropico and Stronghold. One's got you playing El Presidente of a Central American island, the other's a medieval castle building Sim. I haven't played either though. There's also Settlers 7 (but I wouldn't recommend it as I hear it's a bit complex; Also UbiDRM). There's also the Anno games (UbiDRM again) which are a mix of city-building and trading.