Random Ideas:
1) Don't limit how many units you can have in your army by the leadership, instead limit how many from your army you take into combat. So you can have 1000 black dragons, but only the first 4 will follow you into combat.
2) Rebalance melee units, especially those that can be retaliated against, and have low hit points. Give them SUBSTANTIALLY more damage, or damage resistance. Dwarves, foremen, barbarians, berserkers, dragonflies, etc... most of these units are just not worth using because Melee units are so inherently weak in their mode of attack.
3) Make ranged units have a MAX range. It wouldn't be so bad with melee units if the 'ranged' ones weren't infinite range. Even doing half damage they still do so much more.
4) Make more ranged units actually HAVE a melee penalty. I think the only one in the game that does is the bowmen. Either that, or make it not 'the norm' to have a melee penalty and then give bowmen a trait making them specifically do less damage in melee.
5) Give some units weakness to Poison.
6) Allow druids to cast "Overgrowth" ability that resurrects plant units.
7) More unit variety throughout the early game! Only problem with both AP and TL that I've really got, is that you NEVER get certain classes of units in the early game. I wanna try out a small army of demons some time!
Berserkers aren't well designed. Humans would strictly rather have barbarians, AI would strictly have berserkers. There is almost no interesting overlap.
9) Make Bless cost less, and/or last longer.
10) For 'wife' or 'armor bearer' style units, make their starting locations randomized a bit. Add s'more variety.
11) Give single unit summons +1 Morale for each point of Summoning Skill.
12) Include better descriptions for items (A lot are poorly translated or just baffling).
13) Create an 'auto-save' for each new game, so a person can elect to restart that same game.