What didn't you like about Civ 3? I didn't like that game, but I do like Civ 4 and GalCiv2.

My two main issues with Civ 3 were the insane corruption, and the need to bury the map in roads/railways. There were other dislikes, mainly things which I felt Alpha Centauri had done better and Civ 3 had failed to learn from, such as the very limited government types, the unit and battle system, the diplomacy, the more limited victory conditions, and the way all the factions felt so similar.

So if your niggles with civ 3 match mine, then you may like GalCiv2 (or Civ 4!).