So I played a couple of games of the alpha/beta over the past few days.
Some initial thoughts:
The game is visually stunning with an awesome soundtrack.
The politics system is awesome, and really affects your gameplay. Although I feel like I have trouble guiding / influencing it as the player. I especially like the way you can absorb minors into your faction, but at the cost of more complex politics. I know Frog has mentioned that GalCiv is getting a politics system - you should definitely play Endless Space 2 for some inspiration!
Their trade system is also a LOT better than GalCiv's. I love that trade companies level up, and that you can expand them. Also they trade in actual resources that you use to build fleets. I wish the Endless Space devs had actually spent more time on this and made it the base of the economic system, rather than about half as it is currently. I also wish you could trade with other civs (it doesnt seem like you can - unless im missing something?). Anyways lots of great ideas for a GalCiv3 expansion to... ahem... appropriate and improve upon.
The quests within the game itself really give life to the galaxy and give you something to strive for beyond just expanding in the earlygame
No clue if they've tackled the lategame boredom issue that plagues 4x games.
Every time I played I ran into overpopulation issues. Either I am missing something, or its a fundamental flaw. Also one of the races influence growth is crazy and unbalanced. It is in beta though!
Generally though the game feels very polished. AI seems solid as well, although I think the AI for that game would be much more simple to write due to the constraints of the mechanics.