I really like alpha centauri a lot, but it didn't do nearly as well as the civ games. probably just ahead of its time since it was a great game.
It was great...in some ways, it may be the best Civ ever. The sci-fi theme may not have the same appeal, but it had lots of awesome elements at work. The unit design workshop, the terrain differences, and the way it implemented government--all fantastic. I wish they'd left those things in place in Civ 3, 4 and 5.