Fantastic sound design. The creepy sound effects are appropriately creepy for a game that takes place below the surface :) but the sound of the bass and drums is excellent too. I think my favorite part is the really subtle midrange pads around :40. I really like subtle stuff like that, I think it shows really good taste and musicianship.
Hey, you know that clap/snare at 1:30? Why not try adding more reverb - could give a lot more atmosphere to the piece.
Sadly there isn't much in the way of melody/composition, which is preventing me from giving a higher score - but as a background piece in a game I can see this being super solid. Nice work.