Really great work here. Your lighting is awesome, there's just a few little things I don't think match up with the rest. First off, I'm going to assume that this is a woman, if not, then my second point won't really matter that much.
The hair looks a little thin, looks as if it's been done with a brush, and then no more. I'd like a little more depth and detail here. Secondly, her hands are a little oversized in my opinion, and they also look a little too beefy and manly. Otherwise it's amazing! I'm gonna show my fiancée this, she does a lot of digital art too.