The concept is very interesting!
I think it could be a nice idea to add more graphical element to help the player to know where he is. I passed so much time to find the last pill because everything looks the same.
Did you try to use more predictable movement for the gun? It fit more the theme with random movement, but i'm curious to see if it could feel better if the player can anticipate the direction of his gun.
I really like that you decided to make your own art and I had fun playing your game. Nice work!