Overall not that bad, but it doesn't really stand out as an "only one" game; You have different bullets that you can shoot once (but recharge infinitely); and The boss has more than one phase completely overhauling his mechanics to boot
Viewing post in One boss, One room, One shot jam comments
So first of all the aiming and shooting is really good;
But the enemy really doesn't make sense at first; he just floats around and does nothing;
I am not really sure how i'd improve it, but I would probably make him shoot since the start making it a scramble to find the ammo;
Also I'd make the enemy die in one hit and the ammo not respawn;
That being said it's just what i'd do; I am not sure that this would be the best experience that you might have intended :)