Realistic Character modeling - Second try..

Hi guys.. this is my second try in realistic character portrait..
I have been working on this for past few weeks.. for modelling I used zbrush, maya, wrap.. texturing in mari.. rendered in Arnold..
Maya is getting crashes when I tried for higher resolution.. I am not much happy with the rendering results..
Can you guys give me feedback and suggestions for improvement.. I am a self learner in this and I am from a different profession... modeling is my passion..