Good point Mordheimer - maybe a few splashes of colour would help add some realism to the piece and create some depth?
Smoke stains on walls, or the posters found here would add some character to the vertical surfaces. A mixture of PVA, water and paint makes pretty good gunk puddles and can be whatever colour suits you, although green would probably be my suggestion.
Very nice stuff and as Mordheimer mentioned, my criticism is intended to be constructive not destructive!
Regards,
Jammer