Gah! So badass. I can't pinpoint it, but there's something about this that really clicks for me. I think it's the combination of all of the different elements: the pose, your lines, the way she really looks solid. Awesome.
Impressive - her stance really shows the confidence of the character. The skeletal structure is really put together right, something a lot of artists seem to forget. One thing though, and I don't want to sound like I'm nitpicking, but Black Canary's sleeves are (currently) part of her jacket, which she wears over the rest of the suit. The sketch looks amazing, though!