I feel like the game is a bit too difficult. But this might have been due to the fact that all the controls are in one hand. Since you don't use the mouse for anything I would include both hands in the movement or have double binds to let the player choose. One example may be to steer with the arrow keys and use C and X to fly up and pickup boxes.
I think the art is very consistent and greatly highlights what's important.
I am no music expert but I like the fact that there are multiple tracks.
Great game!