Ok, discussion time.
1. Armoury no longer gives instant access to tier 2 units (Axeman, Gunman and the new Lanceman) to unlock the tier 2's you have to research them at the armoury which takes 1 turn.
This change adds some extra balance to different build orders. The meta was starting to shift towards armoury being the best tech to invest into every time, It still kinda is but you need to have a decent econ advantage to start rolling out the tier 2's, it also adds an extra decision of which type of unit you want to invest into (Melee, Ranged or Cavalry) which is a bit more deep than just unlocking all of them at once.
2. Rich mines have been changed from +40 per turn to +30 per turn.
Rich mines getting nerfed in my opinion is an ingenious balance change. The meta was becoming very focused around barracks 1st and builder rush strategies since the rich mines were such an important part of the game. Going for normal econ was a desperation move. This change brings double mine back into the meta as a valid strategy and makes the amount of mines you build a slight bit more important than what type. Building safe econ is now a much more valid strategy.
3. A new barracks unit, The Horseman has been added.
Ranged units were starting to feel like the more powerful units compared to the melee units, they did have less health but getting in and actually being able to do any damage to them was a challenge, especially with move scouting being a thing. The horseman can camp just out of the archer's range and close in and get the damage in. This completes the unit RPS of Melee > Cavalry > Ranged > Melee and makes the units a lot more balanced.
4. Minor unit stat tweaks
These tweaks just refine the RPS a bit more.
A little thing to keep in mind is that scout can even up any engagement when a unit is up against it's counter as pointed out by J-Rex. Also scouts have been buffed with the ability to see over walls (but not void if you mapmakers want to stop scouts from seeing over certain areas). Also cannon is nerfed even more with a 3 turn build time.