For starters, I'm not good at critiques and its my first one here so sorry if it sucks. And for the record I suck at explaining so very very sorry.
This piece is wonderful but I think that you should blend the shading to make it look natural (you get what I mean right?). The technique you used is really nice, the background is pretty cool too. I think the only thing I really wanted to point out was the blending of the different shades of the colors. Overall everything is amazing. I especially love the bright blue eyes ^^. Hope you get the explanation.
I really like this piece of art , especially the fading type background. The hair however seems almost a little see-through, where I can see the blue and all coming through it a little bit, and partial on some other parts such as where they hair voers parts of the eye and eyebrow, I personally would have made it a little darker. The affects on the mask are really good though; i especially like the string and the theme of him being unmasked and all that. the other eye (the far one / left one) seems almost a little disproportional in comparison to the right. However, I really enjoy the right eye as far as size, emphasis and colors go. Over all, this is wonderful. great job