It's a funny game. It's very innovative. By the way, I have some advice you can consider and maybe your game will be better!
I think that using the real physics 2d box is not a wise choice. When I firstly played, I was stuck int the beginning because the box rotated and then blocked my way. Next, you can make a pause button or use Esc key because when I firstly stuck in the beginning, I can't restart and have to close the game and start it again. Finally, I think the check points are a little bit unfriendly. When I died in the second boss battle, I will transfer to the point where I pick the shield.
But it's a nice game. Good job!