The theme was respected and the game mechanics were interesting with the reusable projectiles. It was also more interesting when another opponent spawned. I expected the balls to bounce but it was ok. I had an issue with enemies spawning on me so maybe make a collision detection around the player and if enemies wanting to respawn are inside of it make them not spawn. Since they wouldn't spawn if you stay in the middle you can add more spawn points too.
I hope these solutions would help you, cheers!