Ok...lets see...this is my first post here...
please comment on my work ^^

http://img405.imageshack.us/img405/7503/nagato1024x768ot9.jpg

Did you make the vector as well, or...? I'll mostly refrain from commenting on it, but I must say that the tears look somewhat too... oozy.

Although a simple background doesn't mean a bad wallpaper... as it is, it doesn't match the foreground in any way - be in tone, be in theme. I'd suggest either working on it, or coloring it to match Yuki's color scheme better.

Your vectoring skills are awesome! try to change the background its TOO simple! since she is crying, try to put essense to the bg. dont put the book it doesnt relate to how she felt nevertheless if she was hit by the book.

I love this showw...although, the first episode is mad confusing...>.<

Hi, just thought I'd leave my 2 cents.

You have some slight pixelation going on in Yuki's hair. Try using a smoothing tool to work that out (depending on what program you're in. I assume you're using something like Photoshop).

The background does seem a bit disconnected from the image of Yuki to me. I mean, the girl's crying, but the bg is a bright cheery blue. The book looks very random to me. I know that Yuki's a bookworm and all, but it doesn't seem to be fully incorporated enough to call it a logo, and so it's just kind of hanging out...

Try thinking about what you want the wall to convey, and they making a bg that expresses that and fits with Yuki's image. You'll be happy with the result!

To be honest...the background i kinda did it randomly =x

In my person,this wallpaper is too simple,and it's color takes only blue and little girl's face feel strange,but i believe if you can try more times,your wallpaper becomes greater and greater!

Here is the one i re-did

http://img295.imageshack.us/img295/8164/nagato1024x768hj5.jpg

Um, is it suppoused to be a window? looks like a comic book. Try to get some wood texture on the white stuff. Unless you wanted it to be that way O_O
Also, I'd remove her "reflection" because it doesn't quite look like it. Or maybe making it smaller, but then again the angle would en looking weird anyways.
I agree that the tears are like... too dense,try to find other pictures of girls crying, maybe if you didn't shadow it with a gradient and soft technique? A more clean shadowing might help (you know, like anime sweatdrops XD) You could try making more tears too, falling on the pillow.
The stars are a bit too fake, you can a) use more variated brushes and sizes and colors and trasparency or b) look for a starfield tutorial in google. you'll find many.
Finally... try to lower the opacity of the shiny part of the window, since it looks to strong for some reason.

This is a weird sight for me though, Yuki crying...
Hope I helped you =)

I have to agree that the window does in fact look like a comic book panel :x, and the tears look strange, but i think the reflection is a nice touch and you should keep it! Maybe less stars too, thats quite a bit!