I took a look on the city pictures, here are the things that I noticed:
1. The the size of the city graphics is larger in comparision to the size of CTP1/2 city graphics. Therefore you have to shrink them down a little bit. Maybe you could ask Martin the Dane if it is possible to make a *.til file that contains larger terrain graphics. Than you could keep the size.
2. The colors of the city graphics are not very bright. I like brigth colors. But that should be no problem if you don't like bright colors.
3. There are no shadows for the city graphics, OK for the cities it dosn't hurt so much.
4. The Civ3 *.pcx files are 8 bit and 255 colors pictures, the CTP2 *.tif files are 24 bit including alpha channel and 16 million color pictures.
5. The CTP1/2 sprite format is a compressed format in comparision to these Civ3 *.pcx files that looks uncompressed. Therefore my conclusion Civ3 needs a lot more space for graphics than CTP2 and the quality of these graphics is a great deal below the CTP2 standart.