Some of my biggest gripes about "realistic" Poser renders are the poses - body language should look natural and fluid (but this is also in part due to rigging), lack of carrying an expression through the entire face or the entire body (where appropriate), and the fact that most have the characters looking directly at the camera.   I think if you conquer all three, you're going to be happy with your result.

 

That said, I don't do any "realistic" rendering in Poser. I like more stylized rendering.