Nice setup and composition... just a bit too dark, in my opinion. (Perhaps a lighter background or brighter lighting would have introduced a bit more 'snap' in the shot.)
interesting setup, but i think it falls short of its potential. a couple of thoughts: i'm not sure why you felt you needed the mirror on the bottom, but in using one i would have taken a large mirror so the edges were not visible in the photo, and it looks a bit dark, i assume because you wanted to avoid reflections from the light source, but if you had boosted the saturation a bit the m&ms would have come out a bit stronger.
Excellent composition, and I like your lighting - no weird reflections that distract on the glass. I think this could have used a touch longer exposure, though. If it were a bit brighter, it would really make those colors pop.