Jay, you have a good basic understanding of line weights, shadow, and proportions.
I don't know your age, but if you'd like a full critique done by me, please PM me then I'll critique it over the forum. I try to use constructive criticism when critiquing, as it's the best way to learn and get better (from personal experience).
Not nay-saying about the "talent" thing guys... But drawing is really only about 10% talent. The rest is practicing and perfecting. I can tell that you've been drawing for a little while at least, maybe for a long time... If you'd like some more of a "professional" opinion from a design student then PM me.
This reminds me how much I want to get my portfolio into an online version... Unfortunately most of my stuff is on 18x24" paper and I don't have a scanner that big.