Can I give you an honest opinion?
I think this has huge potential and you're almost there on the right track - but this is not finished yet.

Lovely concept and great colour choices to set the mood right. So you've got great start there. The painting isn't bad either, I like the similarity with Makoto Shinkai's painting style, not sure if it was intended or not.

To me the biggest let down was the silhouette and the stars. I think the stars should be painted as well to keep everything looking consistent. And the silhouette needs a lot more detailing on the characters and the landscape. Or perhaps rearrange your stage so it's more sky-oriented, that the silhouette doesn't take so much space so the solid-fill black isn't as dominant as it is now. Something like this: http://www.animepaper.net/gallery/wallpapers/topwallers/item25982/

Anyways, well done for getting this far and good luck with the group, looking forward to more Makoto Shinkai goodness :)

Oimgyahh! A Makoto Shinkai wallie! I need to see this one still! Nice job on the painting, but as supermonchi says, the stars don't really match the rest of the sky, especially the clouds to the left. I think that there could be more of... something to make the whole wallpaper look more whole... like... well I donno haha, but the texture (or something) of the silhouettes kind of... don't look like their a part of the same painting.

But ah, I'm so happy for this wallpaper hahah. Makes me want to finish that one that I stopped a few weeks back...