Taxes - not enough choices
I think it took me a while to realize how badly the unrest situation that occurs in practically every city you build was affecting production. The fact that it's very hard to connect cities without spamming pioneers just to get rid of the 15% unrest doesn't help, but I was surprised that I could not set taxes to anything less than 40% without setting it to 0%. Maybe I missed something, but seriously, is the math too hard or something. Many times when I get a Hero with the merchant ability at the beginning of the game, I'd love to set the taxes lower to help grow my cities, but there doesn't seem to be any way to balance this.
Why not a 20% tax rate with 10% unrest?