I think the problem with the hair is the same size of each strand. Try adding thinner and thicker strands, and maybe a few single ones. And for the color I'd suggest to try a less yellowish one. Adding a few other colors (more and less saturated) will help to get a more natural blonde.

Edit: And to get more depth in it, take care of the lightsource. Light on the face is from the right, so the face on the left is dark. Why not darken the hair as well ;)?

I like the hair, but don't like the dithering on the face - dithering suggests the impression of roughness of the texture, which is not good for the skin.