Since your environment is cloudy, you should tone down the shadows on your trees. Your 2 reference images show this, their are no sharp shadows to speak off.
Looking sharp, man. Not a fan of the clay renders tbh, moar shiny. Should be easy to nDo the holes in the front of the upper receiver for the barrel and gas tube as well.
This looks GREAT!! Just be careful with the value on her face. It's looking very sharp. Don't worry about it if this was intentional, but i don't notice this anywhere else on the model.
Part of it is probably just because of the way you created your content. Sharp edges just tend to do this, it's always a better idea to soften things a bit.
add some love to the spec up the brightness for it and up the gloss for the more reflective parts. then in marmoset pump up your specular sharpness. that should help alot