You did a wonderful job. The game feels fresh and polished.
I do have a small problem however. I feel that Authority and wide empires are overpowered.
When i get a militaristic opponent (on Emperor). It does conquer civ after civ, and there is nothing i can do against it, except killing it.
The +6 production per city is pretty significant in early game. Starting up new cities are very easy that way.
Is there a way to change the 10% cost increase per city on tech/policy?
Or make it progressive like this: second city 10%, third city 12%, fourth city 14%, and so on.
Puppeting cities also need some thought in this regard. (remove it alltogether?)