This is really nice stuff. Your concept work is very good.
Your figures tend to have the same pose, and it looks a bit stiff. When you get to the extremities, like the head and limbs, the anatomy tends to turn wonky. Especially the lower legs, the hands, and the facial features. You definitely need to fine tune your anatomy work and it will help you a lot in your concept work. I would like to see have more variety in your subject material. I think you should change it up sometimes, and try more dynamic poses, more flesh tones and different fabrics for clothing, different hair and bodies that don't hide under armor.