The game is really fun to play! The cube's squishing was really satisfying, and the overall art was great too!
The game did lag a bit when I pressed the Enter key to restart.
I would suggest to make the grappling gun's aiming a little better, maybe use the mouse to aim the gun as it was already mentioned in the comments (but I see that you decided to use AD keys to bind the aim and movement keys together to fit the theme).
Overall an awesome game!