I love the intensity of the eye, that turned out really nice!
I think what's bothering you is the line from about mid-nose down to the chin -- there's a bit of distortion right above the mouth, and he looks a little like he's got a fat lip. It's not a bad effect, but if something's not right to you, that might be it. (I'm a proofreader by day, assassin by night so finding glitches is my bag.)