What was the nature of the company you were submitting these to? Game company?
What strikes me first about these is that I'd have a hard time modeling these things if I needed to. Remember, concept art's main purpose is for a modeler to use it as a guide from which to make a model.
A good modeler should to be able to fill in a few holes in a 2D concept, but in this case they'd be doing a *lot* of ad-libbing. They'd be doing way more of your job than they ought to. Detail and specificity go a long way.