I got typified as a "Brave Gamer" (interesting, what's this about?). I played on normal difficulty.
I almost never play/enjoy bullet hell games, but the format of your game is interesting and enjoyable to me - it gives a sense of a lonely world that has a past to discover, so I feel encouraged to explore the game world and learn about its contents.
I sort of "missed" the defensive treasure that increases HP to 3, then attempted to fight the first boss of this version of the game - failed 16 times. I backtracked, found how to get it, and then defeated the boss on the 17th try. The difficulty feels appropriate here.
I feel that the second boss (took me 20 tries with my HP at 3) is quite a jump in difficulty compared to the first boss, and felt significantly more difficult than the third (I beat the third boss on my first try). I believe this may have something to do with the rotating hitbox lines that force the player to move in circles around the enemy; the first and third fights don't have that, making them a lot easier in my opinion. I'm not sure that these boss fights are necessarily done in this order, but hopefully you can understand what I mean by my descriptions.
The game ran fine for me, and I played with a mouse/keyboard. The controls/menu navigation are pretty easy to understand as they are.
I liked the NPC interaction, and found myself wanting to interact with more, though the lack of them does give a lonely atmosphere to the game that is nice. The soundtrack is provokes the imagination and adds a lot to the atmosphere. Also, I noticed there's no combat outside of boss battles. Will there be combat other than bosses? I would like to shoot at things other than bosses and switches, but a boss-centric game might be pretty cool too.