I think more units need to be balanced to be more like the halberdier. At level 20 he has like 1k hp only like 150 damage and depending on the formation you set them at, 85/85/30 or 60/60/50. This said, he fills his role, a tank, he absorbs lots of damage well and doesn't do much.
A unit I would like to see a buff to would be the maceman. He never achieves much even when you give him an amazing chance to prove its not crap. Due to his weakness and inability to absorb damage, I would like to see a speed increase and damage increase to this unit.
As far as cavalry for men goes, I think the easiest short term buff would be to change the damage they deal to crushing. Most units in game are not really made to take crush damage and could easily help the forgotten units be used more often. If this is not an appealing idea, then just simply increase charge damage as the unit levels up.
I would really like to see combat in the game take a warcraft 3 approach. The game had many different armors and attacks that gave the game a really diverse feel over a small amount of available men. Heroes had stats where normal units did not, and they had many powerful abilities making them extremely valuable as the game progressed. In effort of keeping battalions and formations appealing, I feel they should have larger bonuses, while units have less stats. That way if a guy activated a formation of a certain style you had a reason to be worried about it, rather then going well this doesn't do me any good.
The final blab of the day, is to see something new, like squad linking. (Suggestions favor man) For instance, imagine placing knights in anvil formation, and then tasking archers to them. The archers would then take their places inside the formation and become very well protected from melee (Archers gain a minimum range to balance this). Perhaps you assign archers or crossbowmen to swordsmen and they take up a skirmish stance. The ranged unit would stand in front while the swordsmen close behind, as melee and cavalry close in or start damaging the ranged units they will attempt to fall back behind the swordsmen (This is going off the idea of having snares or unit locks to stop units from running past people). Or maybe a combined charge idea, where lance style cavalry charge in and knock down and disrupt units. Cavalry with shorter weapons (maces, swords) charge behind and deal bonus damage to the hit units.