This is a promising game. It still lacks further refinement, such as making the movement smoother and fix the song looping on top of each other. But as to gameplay, it lacks chalenge. The game itself is too easy to beat and the cats pose no threat at all due to unlimited ammo, 1-hit kill and their totally predictable movement.
My suggestions are to add some random factors to their movements as well as a variety of enemies... Not to stretch too far from the mouse-cat theme, you could make so that different cat species have different powers, add a limit of ammo for each level (maybe) and nerf the thorns. Making the maze more difficult and having different kinds of cheese giving power-ups would also be a good idea.
This certainly has room for improvement, but for a first try it is a pretty decent job. Good luck on future projects.