Okay:
Other than that green color you have in there, I love the colors, nice job!
The forehead looks very odd. The brows are bighter, suggesting that they are jutting out more, which give a very odd look. The bridge of the nose should be on the same level as the
eyes (oops) brow. (see edit)
(I also added wrinkles to the forehead.)
The eyes have a white pixel in there. this could be interpreted as a shiny spot, but I see it as the whites of his eyes.
Looking at it this way, he seems to be facing straight towards the viewer, while avoiding eye contact, a common sign of stress.
I took that part out because I thought it didn't really fit. But if the stressed look was intentional, just ignore that part of my edit.
The cheeks seemed odd to me. I changed it by raising the highlights on the bottom of the cheek to create a gradient to make the cheekbones a bit less/more prominent, depending on how you look at it. I'm not sure entirely how helpful it was.
I also changed the light source a bit, just out of personal preference. I think it really brings out his eyes.
