Holy shit! This is pretty incredible. Some really striking shading, and tons of little details that make it interesting to look at. I love pieces like this.
The one little nitpick I have, however, is how it's cropped on the left side. I feel like it would look so much better without part of the Octopus' head being cropped off like that.
Aside from that, though, this is fantastic! Great stuff. :)