You're game is really fun!
I played untill the co-op part because i am only one person :P
i would recommend three things...
- some hitboxes feel a little bit unfair so i would like a little bit more foregiving hitboxes
- You can get stuck by pulling the "sticky boxes" between you and the wall.
- adding a retry button is nice so you don't have to go back to the menu to try again
But i really liked a lot from your game. The retro vibe goes well with the simple puzzle gameplay and the way the features are slowly introduced is very nice!