Starts off simple, but things escalate quickly! Well, I played the updated version, so it seems like things were sped up a bit. I do think the bosses still have a lot of HP.
I really liked the progression though... starting simple, building on different attacks, and getting more complicated with each step up! The music notching up with the difficulty and boss ramp ups was a great touch too!
I had a lot of fun playing this, great work!