Hmm... Everything here looks good. I would have placed his left shoulder back a tad more to make him look less tense and more fluid as he sings. Usually, vocals don't shift that shoulder forward unless they are holding a microphone to their lips, otherwise they want their back straight and their diaphragm free from being restrained. (Wow, the things you learn in choir that can be applied in drawing. lol) I really like how you defined the light details under the shirt and the background has a really good effect--gives me the impression that this is a screen cap from a section of a music video with the light cut-out shadow and the breaking rectangles.

Also, regarding another comment you made on another post, I think you can make your mature characters look more mature by adding fine details in here or there. For instance, you could make more whisps of fur from his ears along the bottom (Something I learned from looking at Frosty.) and possibly a tad of it at the corner of his jaw where his hair is. You could do a stray strand of hair between the parts in his bangs, just one or two thin ones that just warrant large enough to place color, and doesn't have to be the full length of the bangs. These together can help you give a more mature look? Not sure if that's the right wording. But you could try it and see if you like the results. ^ ^