I really like the mood and atmosphere you've created with the pic. Very successful in that aspect.
The first things I notice:
One, his head is much too big. It dwarfs his body and just gives him the impression of looking weaker. Think big, broad shoulders in proportion to the head for a more powerful-looking figure.
Two, it seems like you shaded Doom's armor the same way you shaded everything else. Think about how to show the viewer the difference between the cloth of his cape and the metal of his armor through your pencil work. Shiny metal shadows are a lot harsher. Look at some chrome for an idea of what his armor could look like.