I have a few suggestions..
1- More than a way to enter a castle/town, i mean; instead of siege towers/ladders some of these things http://www.earmi.it/armi/glossario/immagini/ariete.jpg Sorry i dont know how to say it in english D:
2- More weapons

!
3- Some kind of "turbo" for the horses lol xd
4- The siege tower move by itself D: idk, some peasants or workers pushing it?
thats all D:
if i think on something more i will edit

cyas