I'd like to see traps in the game. In the stronghold games you could put pitch on the field in front of your castle walls and set it on fire with flaming arrows to kill your attackers. There were also things like rolling logs over the castle walls to kill the guys climbing ladders and people below.
I think that having traps would add an interesting tactical element, and each race could have some race only traps. They could be used to further differentiate the different races and how they fight.