I grabbed GalCiv II and the Expansion at the same time, it was only $40 for both.
I've never played "vanilla" GalCiv 2, but i do love it with Dark Avatar installed; there are still so many things about the game that i'm just working on wrapping my head around; but it's probably right below Civ IV in this genre of gaming for me. I greatly prefer the way it does combat over Civ IV, but i dislike how it does Tech Trees in comparison. But the overall feel is vastly different considering how limited you are in the placement of planets and space stations.
I've only played a little, and i feel that it was well worth what I paid, i know in the future i'll probably sink hundreds of hours into it.... whenever i have time.