The economy was completely different.   The PQ of a planet affected everything:  the productivity, the taxes.....    If your PQ was below a certain level, you made zero taxes off the planet, so everything you spent was deficit.  Some planets you could still colonize, but you had to terraform it to above that acceptable PQ before anything useful would come of it.  If you found a PQ26, that truly was heaven.  No asteroids (that was DA).  Less races--I think it was the Drengin, the Yor, the Altarians, the Terrans, the Arcaeans, the Torians.   Before the Altarian Prophecy expansion, there were no campaigns, only sandbox.

From what I have read in GalCiv 1, victory was determined by who could get to the larger more powerful ships first.  Those ships were predetermined (no ship builder) and you could only play as the humans.  I've been playing GalCiv 2 since Dec. 2005 and I've yet to try out all the new content of the expansions.  TA gaves us unique race tech trees so now each race truly does play much different from the others whether played by the AI or human.  This greatly added to the replayability of the game.  I haven't even gotten to any of the mods!  I think GalCiv II will remain on my hard drive for years to come.