This was a nice little experience. Knowing that I would have one enemy and one bullet made it feel quite tense, as did the ambience, and the creepy nature of the enemy.
The enemy really needed to make sound though. It could add a whole extra dimension to the game trying to both keep away from the enemy and try to find the way out, or to deliberately hunt the enemy down so they are dealt with, ready to then search for the escape. I'd also make the ambience a little louder, as your own footsteps are super dominant.
Some variation in the environment might help with navigation too, although I don't know if you want to make that any easier.
What is in the game works really well, and you did well to put it all together on your own. Good stuff!
Thanks for sharing.