First time playing this and is really fun, I played a lot Diablo 2 and this game feels very well, at the beginning I try an archer but the dmg was too low and I died, later I try a sword and shield and it was better but I died due to lack of life potions, so I tried again but this time I found a two handed axe and made my way with it. I was able to clean the floors with the axe throwing skill that cost 10 mana because I use an alchemy table to turn many life potion in mana potions, beat the first boss easy. I played like two hours.
Something I didn't like is the spells the boss gave me, lowering health, mana or any stat in general permanently is something as I player will always avoid, specially if I will invest many hours in a character. I think a better approach is a temporal penalty so the player cannot abuse the skillt, for example:
"Heal 80 life points but reduce your max life by 10% during 5 minutes, this penalty can stack."
That way, the spell become something which cannot be abuse without consequences, but at least the consequences aren't permanently running a character, like those zombies from Diablo 1.
In conclusion, good demo, I'm looking forward to see how this project grow, because it have a very good potential.