After playing for about 200 hours, and assuming one is not using cheats (which I don't enjoy because they make the game boring - in my opinion), I feel there are two overall improvements that could be easily made to the game play (no major mods required): (1) the difficulty rating is skewed toward being too difficult (based primarily on how fast AI civs gather resources relative to the human). I have gotten pretty good at playing and I really enjoy the challenge but I don't think a human being can beat the AI players at "medium difficulty." In order to beat AI at that level, it seems like one must also be a computer and play the game "perfectly." Shouldn't that challenge be relegated to the most difficult level of game-play? (2) Any civilization with war elephants has a lopsided advantage over any civilization that doesn't. If I don't have war elephants and the other side does then I figure it's not worth playing against them since my chances are slim to none over beating them.
Overall however, this is by far the best builder/empire battle game I have ever played. Setting the game on random for everything creates so many interesting possibilities that I never get tired of playing it (which is a first for me at the age of 60!). If the two previous concerns were addressed, that would make this game the best ever in its genera.