The game looks and sounds amazing, the hands reaching out from the walls is actually unnerving and very well done, having no GUI/HUD really helps with the claustrophobia since all you see are the walls overall a very enjoyable GB experience.
My only suggestion would be to maybe let the player know in which floor they are/if they are progressing (Maybe in a similar way to the controls) because it's a little bit confusing. But not that bad since the game is short.
Sadly I did not find the gun...
Keep up the good work!