For CtP2 scenarios you ought to check the file database and news section on Apolyton. The databases of Apolyton haven't been updated in a while so they don't contain all scenarios ever made for CtP2, you'll have to rely on the news (and news archive) if you want to find even more. Unfortunately Apolyton is down at the moment but once it's up again, you can visit is
here. At the moment the number of scenarios is somewhat limited (12 or so in total), but a fair number of scenarios is currently under development.
Personally, I like games to contain new and exciting features and, aside from strategic resources, I don't really see this in Civ3. The CtP series has stacked combat, unconventional warfare, PW, space (CtP1 only) and undersea cities, etc. Add to that the fact that the CtP series is extremely moddable, so new and exciting mods and scenarios are released all the time. Mods that don't just change the defense value of the Spearman ala Civ3, but mods that completely change the game by revamping diplomacy, radically improving the AI, adding elite or wonder units, pirates, random events, showing wonders on the map, etc, etc. All of this makes that IMHO CtP2 is by far the better of the two games.