Octopus shots can be very dificult. I have taken a few myself. In this case he is so well camoflagued and the lighting so flat that he is blending in to the shot and not standing out from it.
If you had included a little more of the tentacle then I could see more curves. But you did not, so I like the curve of the head, the eye cornea peaking out, the sharpness of the spikes.