My edit is similar to Rydins, except I reverxed the shadows beside the "fin" of his helm.
The highlights are in no way good, but I hoped to fix the contrast between the highlights and your midtones.
I don't know if that's what it is, but his "collar" was shaded wrong, imo. Yours makes it look like a dent. I think I've addressed the shape in my edit, but I realize you are using too many colors that have values that are too close.
I didn't touch the antenna, though it needs a lot of fixes, mainly the shape of the shading, which doesn't show a sphere and a slim cylinder.
You could also fix the jaggy lines.
Make it like the above line in the example instead of the line below it.