You've done a GORGEOUS job with the churning ocean. Very chaotic.
I think it's okay the creature's mouth is underwater. The scariest thing to me about sea monsters is the fact that you can't see what some parts of them are doing. A creature like that whose pointy bits are obscured beneath the violent waves would be psychological torture for me. But maybe that's just cuz I have an irrational fear of sea monsters, no matter how illogical that is.
My advice is not the advice you asked for, but you get it anyway: The dude's face looks wonky. It looks cartoony (or like a failed attempt at realism) while the rest of the piece looks very real. In the first post, I couldn't see his face until I scrolled. I went from thinking it was an epic and awesome image, to thinking it was just a "really good" image after seeing his face. Something about the far eye and mouth really drag it down for me.
'Cuz life is full of your regrets, and I should be one...