An Aria wallpaper is always good ^^.

A beautiful scene you have picked, although I think a little bit more stuff could be done to make it better:
-There isn't anything wrong in particular with the vector, although in a glance I think you can feel it is a little too simple/bland. Since this is a very close up shot on Akari, I think you might want to add in some details that the original screen cap doesn't have, adding 1-2 more hair shadows would help, giving parts of the colouring some gradient so it doesn't look too stiff, and maybe some more hair strands at the back of her head (right now it looks a little like durian ><).
-Clouds is cool, although you might want to give some variation to the colour of the sky. Gradient kind of works although they tend to look a little stiff, best is to paint a little or use some lighting.
-The roof thingie on top of Akari is also lacking some depth feeling...

Please don't mind my little critique >< Still it's a pretty wall and has quite a bit of potential.

Beautiful, too!!!