I made an edit and hope this helps you..
I feel the creases should be emphasized but used sparingly to match the simple style, and the shield arm moved into a lower, more natural position~ especially since a shield is so heavy.
I think you could benefit from an extra mid tone colour too...I feel the mid-tone lime green is too bright and the other colours are too far apart in shades for you to shade with them to their full extent. Though I'm not so good with colours myself, so maybe someone with more knowledge can help you out there :x
Anyway, I hope the edit helps~