It's a good thing holding your breath makes you completely invincible because oh my god that monster is annoying. There are tons of case where it just stays with you for hours without moving and you're just stuck until it finally decide to let you go. Combined with the "hold space to hold your breath" pop up keep reappearing everytime he's around meaning you don't even have to keep track of where he is, and it completely ruin the creepy atmosphere that is otherwhise extremelly convincing.
The fog, the sounds, the low-res textures, all of it works really well ! Especially the sonar which is a really interesting mechanic ! I'd love to see a more polished version of the game with a better AI because this game has a lot of potential.