The vectoring here is simple and smooth but I do think it looks incomplete. It seems like you just used 2 types of layers - base and shadowing. You could have added shine to the hair just like your Uwasa no Midori-kun wallpaper, and also you could have made shadow transitions - not just 1 plain shadow layer but something like some parts of the shadow lighter then overlayed with darker shadows so that it won't look uniformly flat.
Hope to see your improvement with the next wallpaper.Nice job!