Bought it myself to find out.

Sovereigns.  These guys are characters that have their own skills and personalities.  Your leader in GalCiv only represents you during diplomacy, and has no individual skills, while here your sovereign is on the map, has personal skills, can cast spells, and can fight.

As such, there's a good bit of creative expression in a sovereign.  Yes, I already created my own.  He'll probably end up dying horribly.

NPC Monsters are everywhere.  There are also non-player factions, which is different - basically they're playing the same game you are, while the monsters are already there and don't build up a civilization.  So that's a huge difference.

I've heard that the city-building portion is much deeper in this one, as well, with multiple paths for the city to take shape along.  I haven't gotten into them yet.

Overall, it looks like it's a small step up in complexity, while running worse and having worse graphics than GalCiv2. 

First play - tutorial crashed to black screen.

Second play - Played full tutorial, no problems, then created a sovereign and a kingdom, played five turns, quit.  No problems.

Third play - Game crashed to black screen.

Fourth play - played for 2 hours - game froze.

Couple plays later, both ending with me quitting out instead of it crashing.  Yay!

I'm enjoying it, even though I'm terrible at it.

Now having a good time with Novice AI and attacking the monsters just to play around with combat and what is strong, and also my sovereign is now a mage.

What do the difficulty levels do?  There's one for AI, and one for general difficulty... what does the general difficulty change, and what does the AI difficulty change?