Looks like you have put a lot of effort into this particular image...a true labour of love.  The only things that I would maybe look into if I was you are some of the material settings.  The rock looks more like plastic and the grey dudes look more plastic than metal (I don't know if they are metal or not, to be honest) and they also could maybe use some burn/scorch marks or something on a couple of them.

The green glowing light....maybe a little transparency ??

Still, a monument to your patience this piece is. :) 

--Rebekah--