This is my first comment but here is my 2 cents for what its worth. the buildings in the lower left, the rainbow, and the floating island all look a bit off to me. i think they are too crisp. it looks like you put a sticker on top of a picture to me. she does not look bad though, to me it looks allright. i don't really know how to suggest to you how to change the bits i see as being a bit off. also the sea and sky colors look fine. i hope that my opinion of your wall helps you out in some way.

PNG format isn't acceptable for wallpaper submissions.
Wallpaper resolution is also not a standard, acceptable one.
Wallpaper signatures are a mandatory requirement.

I like it a lot, but I would add some brushes to the background so you're more focused on the character, not what's behind her. Maybe add some text too? Hope this helps