I love the idea, it is rather challenging - not my cup of tea, my threshold for effort to reward ratio is not on par with those playing dark souls. I think it fits with the theme quite well. As advice - i don't think you should rely only on one of the human senses to try and combat the invisible monsters. Have a combination of 2, or a choice. Maybe at least put in a hint to where the monsters are by creating waves in the water.