The game is really cool and entertaining!
Nerf the parry; it’s way too broken (I literally played 15 rounds using only the parry, just picking up defensive upgrades and healing).

I really like the game, and that could be an interesting idea!
I just think a few things could be changed:
The speed at which a “press and hold” action is detected could be faster (the current slowness makes it harder and uncomfortable to play, in my opinion).
Perhaps there could be safe zones based on the monsters’ hearing range (I don’t know, I think it could be a good addition); that way, one monster might head toward your location while another stays waiting in the same area.