This is lots of fun and I love the art/music. I got to the 3rd boss. My only feedback is that I wish dying to a boss didn't regress you back to level 1. Restarting the level prior to the boss, so you are always just 1 level away from the highest boss you reached, would i think be less punitive to the player. You'd get to use that level as an opportunity to collect better powerups in anticipation of the boss fight. Anyway, inspiring game, keep it up!