I beat the game, wasn't too hard imo but took a little to get used to the controls. I enjoyed that first boss the most, maybe a little too hard for a 'tutorial' boss but it had the most varied moveset. The last boss was the easiest for me, but maybe that's just because i was better at the game at that point. Some of the bosses wind-up animations were a little light and easy to miss. The most frustrating thing was how they would keep dodging my attack by jumping into the air.
The dash controls was a little frustrating, i wish it would let me dash without holding an arrow key. I was also a little confused how the charge only dealt damage to the shield, and not to the boss, would have been nice with two different attacks to mix up the combat a little.
I realize this might sound negative, but really the game was great and i had fun. A nice variety of boss attacks that didn't feel similar. The visuals and aesthetic was definitely a highlight for me, awesome game.