Really awesome concept! I havent participated in the jam and therefore cant rate, but I hope I cna still provide some helpful feedback.
There just a bit of a balancing issue;
-Red enemies always spawn in one of the corners you're not in, this means you can camp in the corner up until infinity.
-There is no difficulty curve. So once you have mastered the game, the is no going further
Of course there also the missing high score. If you're using unity, you could use playerprefs for this (if you have never heard of that definitly check it out, its super easy)
But now, think about this; what if you kill the enemies, not by shooting them, but by moving them into a obstacle. This could make for some waaay more interesting gameplay. Maybe you could still shoot them, but only for knockback.