Really excellent -- love the art style and pixelation shader, the SFX were satisfying, and the gameplay was simple but addicting. The way the box flexed as it jumped felt very squishy and nice.
I think the risk-reward of hitting it off the walls vs straight up and down is very clever and offers some interesting choice to the player. Just brainstorming here but maybe some sort of bonus-point candies floating around might tempt the player to hit the ball sideways?
Overall though this is a super inspiring entry, you really did a lot with a simple idea here. Great job.