Simple and clean juxtaposition. The first thing I said when I saw it was, "Oh, COOL!" If I had to make a criticism, it would be that the shading/highlights feel a bit too soft, at least to me. The lineart and structure is very good overall and makes the characters seem substantial, yet I feel as though the shading/highlights make the characters feel somewhat intangible and not quite as solid as they could be. Perhaps it's how the lighting would actually work and I'm just being a silly silly, I dunno. :P
I'm a fellow contestant, and I'm a tad jealous I'm not finished with mine yet. Nice work here, and good luck!