I followed Tastybreads method and used spackle putty to fill the cracks and add weight and strength to the cardboard. Im thinking about adding a Greener paint coat, but i like my tan paint job. It reminds me of Callous's figure.
Most of this looks great for work from scratch. Maybe adding some details and checking out some more references would improve some bits that need improving, but overall, awesome job. I know cardboard is hard to work with. ;-)
Anyway, the helmet could use some reshaping, try looking at some screenshots.