the base is simple yet effective. extreme highlights would mean either more orange or yellow which wouldnt look good at all IMO. some guys can take the highlights up to white but that would probably require a massive time investment.
Such a neat paintjob as this should just deserve a better base, a couple of rocks/sand... Green and fairy-like grass does not really fit into the dark and gloomy world of WH40k.
Also what my expert painter friend always says to me - you lack a couple of more extreme highlights.
But still overally is a very solid mini.