Not bad dude. Try to work on face proportions and colours - there are so many different blues/greys in the face which make the difference between something rubbery and something life like. Another thing is the brush. Try not to make everything soft or it can again add to the rubbery look. A tip would be to add mono chromatic noise at 400, add spatter filter, blur it a little, set it to overlay and then reduce the opacity. It will add some grain to your image to add texture. Overall not a bad attempt :)