What I want to see is a battle system that is easier to use.
A lot of my complaints are coming from RTW, but I'd love to see an AI that knows how to manage its troops. One of the major reasons I find the AI loses nearly every battle is because they become unable to maneuvre their troops in force. Instead they move troops in one division at a time, which effectively minimizes completely the advantages in numbers. Also, I'd like an interface that is easier to use. In RTW and M2TW, the problem I had was when you were on the attack, if you want all your troops to move at once in a unified charge, you'd have to either tell all your forces to attack one unit, to which they all funnel into one guy, or pause the game and tell each individual unit to attack one other individual unit, which makes me never want to play the attack in the game because it becomes so frustrating. What I want for ETW and future games, is the ability to tell your entire infantry line to charge the enemy in general, as a singular unified force. Also, I'd like better pathfinding in the game. In seiges, I want my cavalry to go get around behind the enemy so I tell them to run around the square, and instead they decide to run straight through an army of 600 spearmen to their deaths. It becomes idiotic, and often I find success in these games is just to aimlessly wander around enemy armies until they attack you because defense seems to be the easiest way to win a game.