1) Superman's face. Also, no one in the comic ever really opens their mouth; if they're talking, their mouth ought to be drawn at the widest that it opened. This will help show the tone and force with which they're speaking.You do have a lot of potential, but you have a ways to go yet. I would recommend focusing your efforts on improving faces, hands, and dynamic poses, as well as maintaining a consistent style. Don't compromise the style you like most for the sake of speed, because you won't get better at it that way.
2) All the art needs to follow a consistent style; pick either cel-shading or soft-shading and then stick with it throughout. The only tolerable style changes are between cover art and the story panels.
3) The backgrounds need to match whatever style you use in the foreground, even if it means taking a photo, applying a filter, and painting over it. Your style also needs to remain consistent regarding which it is - I see a few places in cel-shaded panels that look soft-shaded, and some of the tiny details are out of place against the less-detailed cel-shading style (example: you drew individual eyebrow hairs and eyelashes)
4) Perspective and proportion seem iffy. Some body parts are smaller than they should be, even accounting for perspective.
5) Capes simply aren't matching the movements that the characters seem to be making; flying in a straight line at great speed like in the first panel will make the cape generally flat from the side, though still with the ripples making the end all wavy. The second panel has the same issue, that cape should be flapping behind her, but the way it's drawn looks as though she is standing still for each pose, with the cape draped over her.
6) Some of the poses just don't flow into each other at all, especially that second panel. If the poses did flow into each other, it might be a good idea to apply a slight motion blur to the faded after-images.
7) Hands need work, they don't look natural or realistic.