Well, I see you used a bird wing brush in there... it seriously clashes with the style of Asuka's drawing, and is too translucent. You should try making the wings yourself, or take others mor fitting - Shinta has got a couple useful tutorials on imanimetions.net, for that matter!

The extraction is somewhat rough - although, zooming in, it doesn't look like a bad job per se - maybe strengthening the outline a bit to that it looks more regular? Maybe even a black inner/outer glow could go the cut.

The white aura it an outer glow - it looks plain, and gives an amateuristic look. If you plan to leave it, you make so through brushing, blurring and layer-blending, I think - although it most times looks bad, anyway...

The grass looks strange. I'd suggest you to take a look at Nat's tutorial at Ningen (*points to sidebar*). If you could employ a custom grass brush, even better!

I see the background is a photo. Just sticking it there isn't a good idea - try drawing over it, applying some filters, anyway - make it somewhat match the style of the stock image. Using flare lens as a sun is a bad idea; it's overused and has a quite fake look. Also, it's a dawn setting, and the sun should be positioned acordingly.

The colors are pretty much dead... you should try living them up. Applying a copied, overlayed/soft-layered layer with some blur or median noise could prove helpful.

About the sig... either leave it discretely in a corner, or make it an artsy part of the whole piece. The way it is, it'd just be cut by one's startbar, most times.