If that was in-game, it would look unbelievable, and be very hard to pick out the flaws, but as a static render it is reletively easy to dissect it (lips, beard, forehead).
I mean the guy looks a little... glazed over... but I can't see what's wrong with any individual elements... at best I can only sense something is wrong... but that's only after been asked if it's render or photo.
The only element that makes it look a bit strange directly looking at it would be the left shoulder... the loss of focus looks a tad artificial. Also the upper lip has a bit of airbrush tinge to it; but even pictures of real people have that.
They made him to look like he's wearing about a poind of make-up on his face. Also the way the hair lays over his forehead is a pretty big giveaway. The hair looses focus toward the back of his head.
Pretty good for a render though. Besides the facial feature problems, everybody seems to always use sub-surface scattering as a whole without using it where it should be. Skin reacts differently to light depending on the area I think. Also the background needs real defocus and not just simple blur.
The main problem for me is the hair. The strands are too big and there's not enough of them...it looks like the guy's chin and head are covered by a few big hairs, instead of many smaller hairs (as it would be in real life).
Still, even as a static render I think this is very, very good.
I knew it was a render.
Reminds me somebody once posted a real photo on a CG forum, and posters were quick to come up with all sorts of critiques for the photo saying it wasnt good. You know the usuall ones nose isnt right, hair looks dodgy etc lol