Glad you like it! Thank you for playing our game.
And yes, I think Health Regen is one of the most op upgrades haha; the logic would be that it is a great "early run" power, but doesn't scale very well - since it's just a 0.4 that won't scale up as both player health and boss damage increases. However, since we were only able to do two bosses, the game doesn't get to a point where this is noticeable!
The heal field was semi-inspired by Soulslike games - in the sense that to drink from your Estus flask, you need to choose a good time to do so. Our idea was that to heal, you would have to find the right moment that would allow you to stay in that field for long enough. Definitely did feel a bit underwhelming to use though, and would need a balance pass!