While the idea of a conjoined twin hero and enemy is very interesting, and could result in a fantastic piece of art, I think your execution ended up being incredibly cliche. Your color scheme, and, above all, the fact that the composition is cut in half-one half blue, one red. The characters could be shown from a more interesting angle, with their limbs positioned differently to make the two sides break into each other and create a more involved composition. The pose is very static, as well as the cape(s). I also think the costumes could have been embellished a bit to create something more interesting and dynamic-particularly the hair. You've already pointed out your anatomical restrictions, and I would agree that you could use more practice in that area- maybe try drawing from photos or even life. Remember- anatomy is not just the body. Faces have a distinct structure, and the proportions on these faces are very unconvincing. Oh, I like your signature!