Oh wow, definetly loving this. The composition is awesome, ESPECIALLY for a cover. I am really impressed. This looks like it would be a great story to read, what with the mystery of all the masks and all. I'm very impressed. I really love her pose, it's very sexy but mysterious. Critique? Well, let me say first, I am so impressed with the hands. Wow. But, the arms seem too skinny, especially at the elbow on her left. I think it should stick out a bit more. Her legs also look a bit skinny, but unlike the elbow, I think the knee looks a bit big. However, these are nothing major and I know with practice you can fix 'em all. (I hope my advice helps!) So don't give up, keep drawing awesome pics. I think the ability to make a good composition is a lot more important than anatomical details!