Good game !
The concept is nice and the mechanics is simple.
Still challenging as enemies get spawning over and over !
One thing you could do is to create waves so the player can see their progression.
In my opinion It's more rewarding than infinite enemies spawning.
Note : You did not mention the jump in the page. Once you use it you can avoid so much more projectiles ! Reached 25 thanks to it :P
Good submission overall :)
In case you want to check mine, it's here : https://itch.io/jam/gmtk-2019/rate/462077