First impressions of the shot are that it meets challenge and is composed well.
The plain white background helps with the interpretation of a face but it also makes the shot quite sterile. I think this is the main reason the score was under 5.5. On a technical level there isn't much to say about the shot other than that the lighting could be improved on the camera body a little. Other than that it's fine.
For DPC it's just lacking a bit of "wow" that would get it up to a 6.
If I find out that this was taken with a Nikon my heart will be shattered ;)
I originally thought of doing something like this but I don't have enough gear...yet.