I am so impressed with the fact that this is your first game. Great job on the stacking mechanics. I would reconsider locking the characters movement to a grid, especially since the grid movement is not always consistent (when already moving the character turns around, but tends to lock back to the grid).
Consider taking the game further by adding a tighter gameplay loop and more reason to keep playing. Add more interesting goals, more obstacles, etc...
Nice touch with the disappearing walls!