I love the visuals, and the gameplay feels really good!
I would consider adding a invincibility timer after you get hit. I got absolutely destroyed by those masks that shoot more than one projectile at once and lost all my health on one go. I would also consider making some enemies only be hit by the guy on one side. Since the enemies go from one side to the other, you could be fine just by sticking to one side.
Other than that, great game and great concept overall! I absolutely love the mechanics!