Really nice use of the theme, creative concept, and amazing art, I didn't get used to the controls of the game (but that's just me being an horrible player) also the difficulty was too hard for me as I said.
Really liked the collectables/upgrades, but I would change so it would only start (the upgrade) when you shoot, since sometimes you get it but there aren't any enemies to use it on.
But overall I really enjoyed your game.