The space background was really well done! I also liked the alien boss art, it reminds me of a beholder. It seemed like there was no limit to the speed you could place asteroids, so I ended up being more spammy than strategic - maybe you could add a cooldown or limit ammo somehow? It could also get frustrating being unable to place asteroids too close to the ship/boss - a fixed zone where you're allowed to spawn them might be easier to keep track of, or you could just always have the forbidden placement region be faintly highlighted. This was a great reversal of the standard arcade game dynamic, nice work!