Very fun! About the only thing I can recommend you do is perhaps add in a few more characters or other benefits for completing the game. If you have a short game with only a few levels, it's usually important to have some benefit to playing through it again, instead of just a score system. Maybe have it where you unlock something for being the game on the hardest setting, or maybe completing it with the highest rating possible? Just throwing some ideas other there.
It reminds me of the old Atari games, where you can sit down and complete them in around 10 minutes if you're good.
Pretty fun game, good job!