Very Well Donw!
I ended up hunting up the original picture so I could compare the two of them. And I will admit you have done a very, very nice job.
As for improvements, I would like to see some more stronger highlights and a few stronger shadows. This will really help make the helmet look like it was polished to a high sheen.
I also wish you had a much larger version of this. I'm one of those who like to see everything, and I do mean everything.
Really nice man. really nice.