I like the overal design of the characters and the style appeals to me. I think with some time and practice your style could be developed into something really awesome. On a more critical note, the high contrast of the piece looks a bit weird in some places. I feel that especially the left leg of the hero should be less bright when you compare it to the stomach area. The anatomy of the face could also use some work.
For a first digital piece it looks pretty good as my own stuff was worse when I started out digitally.