All right, let's break these changes down:
In-combat healing can now only be done 2 turns after the damage is taken . After that, lost HP can only be regained outside of battle (probably...)
Most melee units now have a copper level upgrade "Swimming", that allows them to enter water tiles
New abilities: Quake (smashes the ground and spins enemy), Marine (bonus dmg in water), Deep Burn (increases fire damage taken)
Most enemies got their hit points buffed by 1 or 2 points
Some humans got their hp reduced by 1 or 2 points
Apart from this, there's been a bunch of smaller graphical updates of course! most of the work since Christmas has gone into making Chapter 2.
It should be noted that this playtest specifically tests the demo version of the game, which means that not all units are available to unlock!