The grunge brushes are too much, did you actually think where you put them?
I really don't see the point of the strange shapes of the lighter coloured metal parts..
You obviously didn't put any thought into this as there is no explanation that I can think of for the grunge brushes in it, kinda looks like it's been painted on, I know it's armour but there is no way there could be such damage done, it wouldn't be in it's little spot if you know what I mean, the whole thing would be messed up.
The shading is pretty unrealistic too.
Remove the grunge stuff and put a few dints in the armour.
I'd give this 7/10
gl