I see excellent artwork and very smooth controls. The concept perfectly fits the theme.
Here are a few places I think you might want to touch upon- When I collect an item, a quick particle effect followed by making it disappear. When you hit an enemy you just see a floating bubble showing damage dealt; enemy knockback with very minor camera shake would do. Prevent the player from shooting when you are interacting with a UI element. Also, during level generating, I could not understand how the count of the platform affects you, because even when I did not drag the platform the count was decreasing.
Overall, I would guess you lean more towards the art side and you've done a great job being a solo dev!