Things I liked: The art style was on point. Interesting use of mechanics! I found myself wanting to complete every level I could (I did beat the game)
Suggested Improvements (just suggestions, you can ignore them if you like): If there were any sounds, I didn't find them. Feedback sound-wise is important to hint at what the player is doing correctly, and what is going to get them killed. Also, there were just a few minor bugs I ran into. Nothing that a little more programming couldn't fix. If the player starts the game when dragging a box, the box is stuck on the cursor, and can't be dropped. I would suggest making it so that the cursor drops the box when the player starts the game, just to make sure they don't lose the box. Also, if the boxes are positioned right, they can get held in the ceiling, blocking some of those enemies that drop projectiles on you. I'm not sure this was intended, but it might be worth looking at if not.
Overall, neat concept, and I'm happy to say you're the first game I beat today! Thanks!