Civ 3 has sold over 1 million copies world wide. There will be a sequal (read: Civ 4).
As an aside, what would be 5 things that *I* would want from it that aren't currently included in Civ 3; well, here goes....
1) Completely configurable tech tree and starting ages/times/dates. The turn length should be changeable.
2) A concept of national borders that is *INVIOLABLE* without causing war.
3) Ability to create scenarios (starting location, civ, cities, units, etc).
4) Ability to allow user created AI scripting
5) Civlopedia accessable from every screen in the game.
Oh, there are other desires and wishes, but this will do me for a start.
6) Drop in MP3 support.
Tom