For what its worth, for me personally the interface and the economy I could come to grips with. And i liked the economic system in the game. But what I personally could not in a stand was micro-managing battalion sized formation and their logistics in a strategy game of this scale. And assigning the AI control just leads to disaster. So what I would want the most is to not have to control lower then brigade size formations.
I know coding AI:s are not easy, so the alternative of making an AI capable of competently fight as a cohesive force if you group some battalions in a brigade is not something I really expect to happen.
Maybe you could decide to have brigades control a given amount of squares with the fighting power of the brigade diminishing with each square. Good infrastructure could negate some of the effects, different terrain could make these effects better or worse depending on if you are attacking or defending. The combat value of the brigade could be an abstraction of the combat values of the battalions you decide to put in it.
Just my two cents, the point being that what made it the hardest for me to enjoy the game was the military micro.
