Firstly I want to start with saying I'm very excited for this project. Symbaroum is one of my favourite settings, but my friends that I play with are not keen on having to learn yet another rule system (We play D&D 5e and Coriolis). While reading through the PDF a few things come to mind, but I will have to see how it works out when we play it in my group.
- I think you have made a really good job with the Mystic class. I have myself been playing around with how to implement the Corruption mechanic to 5e OGL, and your concept is much better than any of my ideas.
- Your decisions on what spells are on the edge of being dark sorcery or not seems a little arbitrary. When I look at the spells for the wizard Burning Hands and Fireball are considered on the edge of being dark sorcery, but Flaming Sphere and Scorching Ray are not. Yet all of these spells create fire to do damage. Personally I don't see why fire is considered dark sorcery.
- Personally I don't like the system of your hit points being dependent on your race instead of your class. I do see the logic behind this (goblins are smaller and should thus be less resilient than humans), but balance wise and for the game mechanics I think it is better to follow the standard 5e OGL way of determining HP from class. I think a better way to give some minor differences between the races is to play around with the ability scores, perhaps give goblins -1 to Constitution. This opinion was also expressed by one of my players who has read the PDF.
- The text explaining what happens when you exceed your Corruption threshold could be made a little clearer. I think I get how it works with the 5e OGL rules, but for someone that is completely new to Symbaroum this might be a little confusing, especially when you roll on the Corruption table.
- I do not know if there is a big need for making very different classes of the none spellcasters in the game, such as the Fighter/Warrior or Scoundrel/Rogue. But I am curious to see how it end up. But mind you that the classes in D&D 5e have had a lot of players testing out those classes, and they seem relatively balanced and popular.
- Concerning the Warrior I like that you have kept Action Surge. I know that it has been criticised for being "simple" or "boring", but I think that it is good to have simple mechanics in a game as well. If you have a class let the class mechanics be simple, for the players that want more advanced options these could easily be incorporated in a subclass/approach. Just compare the Battle Master and Champion subclasses from D&D 5e.
Lastly I am really impressed with what I have seen so far, and I cannot wait to see the finished product.