Pretty Awesome
I mean, its a shark, and sharks are awesome, thus, this piece is awesome.
Taking a moment here to look at it in a high resolution I must say that one of the most impressive things I notice is the clean line art. Since I'm try to achieve such clean line art myself, this impresses me.
Not only do you have clean lines, but they display weight so well. This one thing alone has got to be one of the best things of this piece.
The lighting on the shark is ok, it's subtle, but considering the ambient light that water tends to put off, it seems in place.
The tail is where things start to fall off the wagon. The jagged connection has a few places where it lacks color. In your defense though, it only is really noticeable to people who are looking for mistakes and in the high resolution. Another thing with the tail is, what is it? after reading your authors comments, I can see it but before that, I thought it was a piece of wood or something. Its not the shape the throws it off but the texture you have. The texture looks like wood grain in some areas, it really does.
Over all I think you have a good playful piece. I think you need to work on your fur textures a little though.
Nice job
4/5
8/10