Well, I'm not that good at bullet hells, I guess... I didn't manage to get to the boss in 8 tries :P
But from what I saw the difficulty seems pretty nice, the bullets and enemies are easily distinguishable. However there is very little feedback if an enemy takes damage, or when the player does.
The game felt pretty fair, although I do wish I had a little more lives.
Over all, I had fun with it! :)