More detail and variety to ports and cities would be nice, maybe even more different architecture styles than the 3 we have now. Maybe some people and scenery like a carriage...
Also the ability to upgrade forts and towers would be nice, with new model.
All pictures are from naval action work in progress except for the last that is and example of how it could look taken from AoE3.
Also more "hidden" places like Kidd's Island just smaller would be nice. I feel like you have this huge map but you don't use the space... Only really cool places I can think of are Kidd's Island and Bensalem. Bensalem should not be on map either and located further away from the coast but it still looks cool.