I like the position of the corner in the frame and the lines leading you from the left and right are good.
Technicals:
A very good choice on your white balance, the different shades of blue has really added an extra dimension to the overall image. There are some lovely textures and detail and certainly for first or second glance I couldn't tell what it was.
My personal thought:
In all honesty I can't find a reason why this image didn't score better! That doesn't help you much for the future, all I can say is keep on doing what you do! :o)
If you've got any questions about this critique, please feel free to contact me via the PM system.
Great shot. Can't wait for your setup details to show up because I really want to know what it is. Perfect sync with the assignment as even after second glance I can't tell what it is, but I really like it!