You really are quite the talent, of that there is no doubt. You have room to improve, as we all do, but your skills are very well developed, and even a sketch like this, without color, conveys your abilities well enough for me.
My largest (still pretty damn small) nitpick would be the hair shading, or rather the formation of it. It is too shadow...y? It is all curved, lighter and darker where it shouldn't be, and against the grain of the cut.
This spider was under-detailed, but that's really unfair of me to say- this was, after all, a little sketch done to celebrate Halloween, I shouldn't be expecting perfection from you. That said, a consistent level of detail does increase the overall feel of the piece magnificently, cutting corners, however small, is going to leave a stain on a good piece of work.
Well. That is actually all the complaints I have for this. I like this piece, a lot, but there are small parts where improvement could be made. Again though, it would be both pretentious and annoying of me to assume there is one person alive who doesn't.
All in all, your piece is great. The line art, shading, and attention to the smaller details pick this out as something quite eye-catching. I'm going to give you 7.5, and wait for the day I give you a perfect ten.