The light, airy feeling of this wallpaper is fantastic. Definitely perfect for summer!
I love the use of dots; it makes a subtle but beautiful effect. Same with your use of texture in the hat and dress.
The vector is great, although jagged in places. You did a really good job constructing the wheat field; just the right amount of depth and detail.
It would have been nice to see some of the colors used in the figure mirrored somewhere in the scenery, like the green of her hair and eyes or the pink of the flower. Miku stands out a bit harshly because the colors on her are so vibrant in comparison to the wheat and sky. Subtly mixing some of the colors on Miku into the shadows and highlights of the background would go a long way to blending the figure in.
I look forward to your next wallpaper!