I like the idea, I'm a fan of submarine 3d games in general. Quite an ambitious approach, to get that photorealism. But I have to say, the framerate is so low that mouselook becomes dysfunctional. I can't center the pearl on screen. The close blur of the DOF starts too obviously. I would add some god-rays from the surface and probably a slight refraction shader or a substitute thereof, not for what's above the surface, but for the water itself. Some subtle clouds , gas bubbles, animated seaweed maybe. But that's just my preference.