Great concept! I liked how the sonar pings not only immersed you in it more but also served as helpful guidance at times. I think with just a little more time to polish it, this could be really great. A more detailed rules explanation or tutorial would be great as I struggled at first to realize exactly what I was supposed to do, especially early on when I didn't know to stalk them and the spacebar UI would only be up for a fraction of a second. The lighting was also a bit rough as it was so bright that it made finding subs very difficult at times.
The stealth aspect was really neat though and gives a fresh take on playing as the monster. Most games like that would have you smashing everything so a more subtle and stealth focused take is a great way to go with it.