-Are proportions accurate?
-Is foreshortening accurate?
-Does anatomy look accurate (esp. things that are hard to draw eg. hands)?
-Is it shaded accurately? Can you tell where the light source(s) are from the shading? If a light source is drawn does the shading reflect that?
-Does the image have depth?
-How well were they able to create a representation of what they sought to achieve?
Not all of those will apply in any given situation though. There should also be one about color (and other things) but I'm having trouble making it less subjective.
karlu20
Skill seems far too empty.
xxxZigZagxxx
It is fairly empty.
Of course the section has less questions underneath it, but that doesn't mean it doesn't matter as much as the others. That said, I'll probably add more to this as I think of it, and if you have any suggestions, feel free to throw them at me.