I think your eye for musculature and shading is exceptional.

Your figues look very sinewy and living, not like flat drawings. I especially like the lines in the torsos. You could almost be auditioning for a Marvel strip with some of these lookers!

The area that I think is the weakest is fluidity---I guess, to put it simply, the motion of the figures--- but I can see really awesome glimpses of it. The little alien dude right above is probably one of the drawing that looks most "real" because you can see how it is "rising" out of the ground, and you are just waiting for it to start sliding (slithering?) away. Your human figures seem a little more stiff, almost posed like action figures.
The outlines and the details are great.

Just a little more work on the movements at the joints, and relaxedness in the posing.
ps. Can I add to the discussion earlier about women's shoulders? One thing I've noticed when drawing them, is women's shoulders sort of scoop in slightly between the neck and the rise of the shoulder itself (and a more prominent clavicle), whereas men's are more rounded with muscle. Concave for women as opposed to convex for men. I think the fact that you have them more rounded make your women's shoulders have a more masculine appearance.