Re-do the shading. Add some highlights. Clean up the black outline.
Add some minor details to convey what type of helmet it is. (Metal, Plastic, Space Helmet, etc.)
I don't think it is the gradient tool though I could be wrong. Seems like it's just saved in a bad image quality. (jpg)
Smoke, I noticed something weird about the image's back view. If you look at the side you have a piece covering the back of the head separate from the piece that covers the side. When you look at the back view there's no piece there. I circled it in the attached file.