First, I love this game. Bought the original and after that the warband expansion.
I play both multiplayer and singleplayer lots of times.
For me the most annoying thing in the singleplayer is the charge:
For example, I get into battle with 25 archers, 15 infantry and 10 cavalry agains a huge enemy army.
I use the formation system to nicely line up my troops. Archers in the back, Infantry about 20 steps in front and cav on the side.
I let the enmey come and thin them out / weaken them with my archers, while my infantry catches everyone that gets through. When the enemy is weak enough I send the order to my cav and infantry to charge... With the intend to sweep up all remaining active enemy forces!
But what happens...
My infantry and cavalry (all of them) go into reverse to chase the 1 or 2 enemies that are running away... Leaving my archers exposed to the enemy charge head-on...
I would really like it that with a common charge that the AI will go after 'active' enemy untis first (so they will charge straight ahead) and then, only when no active units are left, sweep up the rest.