This is really freaking cool

I think it's really good

But, and this is just from my own inexperience, and I'm really not that good, but if you want to improve, overall-and while this my seem really irrelevant- I think you should try to work on the body,- Because from looking at your other art I can see that you're faces are really good, but your body anatomy is kind of lacking. If you can draw both of them at an "okay" level (And then keep on practicing furthermore) as apposed to being great at drawing faces and kind of meh at drawing bodies, you will probably be happier overall with what you are capable of doing. Or at least that's my advice (Sorry that this isn't really a review of this piece)