The shading looks good, and I like the way you drew her face, but there are a few critiques I have. The forearm of the arm holding the gun is much too short, and the gun holding would look much more natural if it was resting on her shoulders rather than how it is now. Also the shading on her stomach could be better, specifically around the belly button where there should be a highlight on the opposite side of the light source. I recommend finding references for anatomy and lighting to help avoid this. Hopefully the links I provided work, newgrounds likes to screw them up.

http://www.marcusdublin.com/GenericHeroFemaleBody.jpg
http://3eof.deviantart.com/art/Femalemodel10-01-394202198