I think what all the Civ games are missing is having a unique weakness for each faction. It could be optional. For example, maybe Rome spawns special versions of barbarians near its boarders. Maybe Greek cities other than the capital are city-states that you have a ton of influence over. Maybe after picking an ideology, Germany declares war on civs with different ideologies. Weaknesses would be tricky to balance, but it would create unique and interesting gameplay. Any other ideas for unique weaknesses?