Very interesting photo. The picture definetly has a center of interest, but is it really a subject? Almost a 3-D effect, I half expect my mouse cursor to fall in the "hole". I would have really expected this picture to do better. I can only guess that it was a little more abstract than some people were ready for. Exposure is good, contrast is good, saturation and hue are just fine. This does break the "rule of thirds" for purists, but it would not have worked as well had the hole been off center. If anything, maybe cropping the picture to a square, to play off the circle, might help. Otherwise I think it is a fine abstract piece, and certainly meets the challenge.
I like the way the sharply-defined circle in the almost-center mocks the notion of subject. And nice colors, too! I think you found just the right amount of sharpness. 8
With the green spot dead center in the frame, my eyes are drawn straight to the center of the shot. It's a good concept, I am just drawn to the center of the image, instead of the entire image.