They have a new armor type, unarmored, which takes bonus damage from siege and piercing attacks.
They also have a new damage type, magic, which does reduced damage to fortified and hero armor, but does bonus damage against medium armor.
They had their damage adjusted, typically downwards.
They no longer gain damage as they go up in level, and gain less hitpoints as they go up in level (but start with more hitpoints when initially built)
Many autocast buffs and debuff costs reduced.
Casters, including Dryads, have had their mana regeneration rates boosted by 30%.
Heroes now have an aptly named hero damage type. It deals 100% damage to everything except fortified armor, to which it deals 50% damage. Hero damage was added so that heroes no longer strongly counter ranged units such as Archers and Crypt Fiends.
Most advanced technology structures had their build times reduced. This reduction ranged from 20 seconds for especially underused structures, to 10 seconds for less underused structures. For instance, the Slaughterhouse builds 20 seconds faster now, while the Arcane Sanctum build time was only reduced 10 seconds.
Flares now cost 75/25 to research, down from 100/50.
Ancients temporarily lose their fortified armor when they uproot, becoming medium armor units.
Dryads now have the unarmored armor type. This change was made to further specialize Dryads as melee killers, but allow piercing damage units, such as Crypt Fiends and Archers, to counter them more effectively.
Dryad hitpoints increased to 435 from 380.
All basic siege units (Mortar Teams, Catapults, etc.) have had their night sight increased to 1100 from 1000.