Amnesia was a huge deal when it came out a couple years ago. It seemed to revive horror in games, which had been seriously flagging. It was a breath of fresh air in the space and now has taken on a legendary status in the genre.
The game's developers Frictional Games have a new game coming out after a break, called SOMA. It takes the horror underwater, pitting you against..well, it is hard to tell. Something undoubtedly monstrous and nasty.
Check out the trailer here to give yourself some heebeejeebeez:
I actually had a pretty similar idea for a game once, so it will be interesting to see how this lines up. I think the deep ocean has a ton of potential in the horror genre that just isn't explore enough.