I played the whole game recently myself. And while I liked the concept and design, I found myself getting frustrated at some points. Not by the difficulty, but just by the design. Mostly because of the mechanic of losing a weapons power after being hit, while bosses and enemies become more powerful after getting weaker. In other words, you get weaker over time while enemies get more powerful over time. And if you reach a specific threshold (such as losing your power down to Lvl 1), its almost impossible to defeat enemies or bosses, causing multiple restarts. This leads to a lot of 'trial and error' gameplay and forcing you to defeat areas or bosses by memorizing how to beat it.
In short, I found myself not having problems based on my health, but constantly fighting to keep my 'power level' up just so I could damage enemies/bosses. And some bosses, such as in the Labyrinth, would knock you down to 'lvl 2' with one hit.
I still liked the game, but it still frustrated me at times.