My 2 cents. My overall impression: Great, really great.
Small things I think that need improvement:
1. Helmet - A coat of satin varnish, more weathering, decoloration, a little bit of rust and dust.
2. Bio-mask - Again, a little bit of gloss/satin varnish in certain areas and touches of red colours around the black pipe insertions for a more natural and organic look.
But, again, a really good bust. Congratulations.