A couple or more points to ponder:
Another bug I've recently found, I was able to build the Heroic Epic or Hero Epic without satisfying what it said was needed which was a barracks in every city. I don't even have one and it let me build it.
Also, limiting the building of a settler to one city was cool at first, but I can see as the game goes on that there are two civs that will have a distinct advantage over all others because they were able to get a couple cities made which were strong enough production-wise to handle making defensive units and happiness factories while the capital turned into a settler factory. These two civs did not have any direct threats so were able to explode in growth while civs that were battling for territory might have been able to get one or two satellite cities up in poorer areas and their capital was still forced to bear the brunt of defense and happiness production. So, AI still needs some tweaking to get that better balanced.
An idea about the settler only being built in one place might be that a later tech opens up the ability to produce a settler without the need for the palace. A good place to put might be the lame crop rotation tech which needs more development to make viable anyways.
I think more needs to be thought about how the tile improvements work, specifically the market. Replacing two food, or a food and a hammer with four gold is steep. Why was this changed? Another issue with tile improvements, there should be a base amount of free tile improvements, just like a civ has x amount of free military units. If a civ decides to produce more than this, then they pay the extra. Workers also need to have the ability to undo a tile improvement. And there isn't a way to "undo" an improvement, you can pillage with a military unit, but you can't undo to help with tile improvement costs, or if pillage is supposed to be the "undo", I did not see it affect my econ value when I had a unit pillage to try to save some money. Maybe a bug there?
There also needs to be a way to incorporate infoaddict's charts into the game. Played with that for a game and it was really nice, but now it doesn't work.
Also, Pyramids have been totally nerfed with the whole worker workrate change. That needs to be changed as well as the social policy that increases a workrate by 25%. Workrate? I mean longest I've seen so far is 5 turns for making a mine. I like the 5 turns deal but something more needs to be given for the production of the Pyramids and the balance of the social policy.
And since I'm at it, anyone else really missing the religion aspect of Civ4. When will that be brought in?
Sorry for the long post, but it's feedback that I hope is useful.