Never heard of Deep Black? Me neither, and even obscure stuff like this doesn't escape my radar. It's in development at 505 Games, and is set entirely underwater where bio-terrorists have deployed strange mechs and world-ending devices which you must put a stop to. It looks quite interesting, actually, promising to shake up the third person-shooter genre with a realistic take on water physics affecting the likes of jet-packs, harpoon guns and all manner of watertight equipment. It's cheapest to pre-order at Game.