Since this is just the halfway point for this game example, there isn't too much you can add at this stage that won't be covered in next project. If you enjoy drawing, you might like to add prettier graphics. The following are some ideas to get you started:
The cat only uses one frame at this stage. You could try to give it a walk animation using both frames that are in the sprite.
You could also add more costumes to the cat sprite for more fluid animation.
Another improvement would be to redraw the maze tiles. Just keep in mind that we check collision based on color, so try to keep it simple if you choose to use more colors in the walls.
You can also choose to separate the visual graphics from the functional ones, as we did with the karts in the racing game earlier. This way, you can go all out with the drawings while still being accurate with the scripts.
Feel free to add to the game and move in a different direction than described in the next project. It's your game after...