Hmm. Here's me referencing another game again, my apologies if it's getting on anyones nerves.
Most games have that one unit besides the hero that is so unexplainably bad ass that you just love using them. Because I don't know what units you have in the game I can't really suggest one, but I would think there definately needs to be a unit like the Ninja's from Shogun Total War, those units you just love to use.
I would like to see crossbowmen, I forget their names, the ones with shields on their backs. When they go to reload they turn around so the shields are facing their enemies, making them excellent against other ranged units.
I don't know how the devs are going with dragons but they should have some sort of underground unit that can travel under the surface, pop up and grab individual soldiers, and then burrow back under. At that time maybe it could be attackable, trying to get back under ground before it gets pelted with arrows or stabbed with swords.
Humans should have some sort of infantry unit capable of ensaring flying units, or maybe it could simply be a crossbowmen ability, to fire a net up and bring the unit down. It could be combined with a fire units ability, they could cast fire on it and set the net (maybe presented as a net dosed in some sort of flamable liquid) on fire.
An infantry unit for the humans capable of forming the testudo or some variation of it would be interesting. Good for fairing against arrow attacks and fire breathing dragons, but then the dragon could sweep down and knock the units out of formation, then they get pelted by arrows. Or, as mentioned above, the unit that burrows under ground could come under neath and gobble them up or knock them out of formation.
All I've got for now.