I don't like the horror games genre, but this game is incredibly well done. I really like the sudden shifts between illuminated and somewhat friendly areas, full of aquatic life, with dark, plain ones which are obviously empty, or... are they?
I like how the shift builds up some comfort just to break it apart immediately thereafter.
This game truly manages to give you terror, yet sometimes... even wonder... especially in the (spoiler alert!) whales and jellyfish area.
I also love how most of the time you're left alone, seeing nothing and just hearing all the fragile components of the submarine, aiding to navigation for you and fighting against the water's pressure.
Overall, I give this (as a personal vote) a full 5/5.