This was a fun game. My first suggestion is to add a tutorial, there are a lot of buttons to learn and what is where and what it means. It would be much easier to start playing, it it was present.
Regarding difficulty balance and enemy design. Overall I feel that you difficulty isn't too hard, but there were some frustration moments. I especially found the bat to be the most annoying enemy, it moves quite unpredictably, and also it is much harder to gauge if I will hit a bat or not, so I had many situations where I either accidentally hit the bat with my body, or didn't reach enough height to hit it.
Final boss feels too easy. I almost never took damage from it, and main danger is adds it spawns during the encounter.
Last thing I didn't like is how my "heal bar" is reduced on hit. I feel like its too punishing. Like if its full, and my health is full, that means I've been pretty careful recently, so when I make a mistake, instead of being able to use that saved up healing to get my health back up, the game almost punishes me for saving that heal bar, instead of rewarding