This is a super-unique idea. I really like the different puzzles and the fact that you not only have to play with the player's size but also the size of the boxes. I also think it is super cool how you need to time it when you push the box past the turrets so it doesn't accidentally get hit.
There's one small criticism I have, and that's that the boxes have way too little friction. In the second level, stacking the boxes on top of each other took me like 15 tries, for one, because they wouldn't be in the position I wanted them to be, and for two, because they could rotate. So even though the green landed on top of the white, it was rotated and fell off.
Besides that, I really enjoy the different puzzles and the level design. I also really like the Game Boy graphics. Super cool. Overall, it's a great start, and I can really see this being expanded upon. Good job!