the skin tone itself reall looks good, maybe it is also because of a clever lighting but yet the skin texture have to be very great too. but intimate parts (nipples and.. below) as well as face are not very convincing.... You need a bit more contrats i thing. A good exemple of nipple textures are the basic ones enclosd in Mayadoll (they are photorealistic and very high res), have a look to have clues about it. But it is a very very impressive first try, keep going on !