Played through 6 missions on human campaing, nice game but weird unit balance.
Knights and heroes are godly top tier, heavy armor and charge means walking through poor orcs. Heroes tank a bit worse but seem to be able to die with no penalty except main hero.
Ballista ranks second, especially after a couple levels with upgrades to 4 speed and 4 range meaning ability to tag anything 8 squares away with huge damage. Piercing armor also helps, not only that but it tanks better than archers too, likely wont survive cavalry charge but is fine after 3-4 hits from archers.
Then rangers are pretty average damage and tanking, but have lots of nice bonuses, no retaliation, +4 in forest, fast with 5 speed and no water penalty (with proper levelups of course), harass status effect, fear effect. Great to take some unimportant 20coin village, tag orcs garisoning it for 3-4 damage, repeat 2-3 times till they run away, go in and run to next village, not so great in big fights.
Then there's archers, which are inferior to ballista in every way though i guess I'd keep a couple in army because there seem to be 3-4 orc bombers on every map. Yes, they can cower other units on computer turn but with that low damage it doesn't make much difference. Only 2 range and low tanking means fast death, good thing computer AI goes gentle on them, usually doesnt target them if you dont leave them alone out in the open.
Infantry, ugh, pikemen/yeomen are like weaker and slower rangers and retaliation means they become unusable after 2-3 fights, halberdiers seem to be meant against cavalry but 3 speed! Swordsmen are just plain lousy and orc infantry doesnt seem too impressive either.
Air units, both human and orc, just horrible. Description says to finish weakened units but they're bad even at that
I'd take a real unit in that slot. Maybe elven faction's dragons are good.
AI could be better too, plays much too defensive, for example almost always garisons towns even when its not benefitial for it, makes some bad mistakes like stepping into river sometimes, but at least seems better than most games.
Another weird thing, between fights all units get restored to full for free. Wounded I can understand, but I'd expect to pay for new recruits.