Yeah. What they said.
I hope that I won't put too many CTP fan's noses out of joint when I say that it really strikes me as a dumbed-down version of Civ2 and perhaps the weakest concept in all of the Civ style games. The fact that the original was released in the shameful state of not-completion that it was only increases my distain for the game.
There. Got my obligitory CTP trashing out of the way.
SMAC is far superior to even Civ2 in any number of ways. One thing that I could add to the folks above me is how much more real the faction leaders are than the Civ2 heads of state. They have distinct personality traits. This comes across in quotes from them including voice-overs and "parts" in the short movies that follow the completion of a wonder (Secret Project in SMAC)
I only have a couple of cautions for you. One is that while you don't have to be a science fiction fan to like the game, it really helps. I do know a small number of people who have gone back to Civ II because they hate SF.
The other issue is the bugs. As an enormously complex game it was inevitable that bugs would happen. Unfortunately, it seems like one of the games biggest backers left Firaxis to form BHG. This means that it is unlikely that outstanding problems will ever be resolved. Your best bet is to get the package that includes both SMAC and SMACX and install the latest patch. It still won't run perfectly, but even so, it is a game worth having.