Really cool mechanic idea! I also liked the enemy doors. Even though the gameplay is basic they are still somewhat scary and menacing.
I also got the black screen bug then i accidentally lost all my keys! Fighting those doors is tough with just one which really emphasized how important retrieval is.. might be too difficult to get them back without taking damage with the current movement speed.
Shows a lot of promise conceptually and gave me nostalgia from a game I played as a little kid. If you want to check out a free retro game that could be inspiring, check out God of Thunder :D it's free on steam and might inspire some game ideas to expand this 'thrown ammo' concept!