Creative idea. I had fun playing!
Some constructive criticism: I got stuck by accidentally pushing the first crate into a corner and not being able to get it back out. Some sort of puzzle reset button or bounds on where you can push the crate would've been good to have. Also, it took me a few attempts to figure out the range of the spacebar attack, so some sort of animation would've helped. And I'm sure you're aware, but some of the graphics had issues with z-axis positioning.