You know what I want? Facing. I think I should get a +25% against a unit that is facing the wrong way. That would be easy to program, now that the game is 3D. And if that unit is faced the wrong way AND out of supply I'd get a hella advantage.
There should also be modifiers to the supply thing. If I'm the Romans and attacking the English and the land that my unit is on is in English territory, but the culture of that land is only around 52 percent English and 48% Roman I should suffer much less of a supply penalty, as 48% of the people there are on my side and would be trying to feed my army.
Also - why is there no weather in the game? I should be able to move my carriers into a sea square that is covered by clouds so as not to be seen. I should be able to start an attack against a superior neighbor during bad weather so that he can't use his airpower against me. A neighbor entering my territory should suffer attrition during winter months. Maybe the game could change seasons with every turn. One turn - spring - muddy and tanks don't work real well. Summer - normal. Fall - muddy again. Winter - Attrition.