A very creative submission that is in the rare genre of sandbox games. The physics engine is interesting, to say the least.
I do wish that levels were more than just box structures, even with the theme of minimalism. Minimalism should always enhance gameplay, not limit creativity or in this case level design, and I think you kind of boxed yourself in with the boxes, pun fully intended.
Also, level selection when there are levels is always good.
I want to say that due to these bits, you didn't fully meet the level of ambition and polish needed for a truly stellar game despite the creativity of the concept and the fun physics engine. Still, a neat little gem in a rare genre that is worth taking a look at.