the fact that the entire UI is changed and harder for me to use, as well the only real way to win against a euro country is to outnumber them 3 to 1, as well commerce is alot harder to manage as your buildings are unique and perform multiple functions so its hard to decide which ones you need more than others, and to string it together, most people are hostill towards you which means diplomatic negotiations are nearly impossible unless you throw money you dont have at them, for trade which wont really benefit you as you dont have many trade goods as they are controlled by the euro and you cant construct the buildings to enhance trade like they can...
All in all I just dont like playin an america's faction as I did in the Medieval Kingdoms expansion.