I've always been interested in the problem of creating life-like eyes in CGI humans. No matter how good the overall figure is, the eyes are always dead and the believability factor is lost. I don't know the reason for this, but I do know that I can add a couple of simple highlights to the eyes and it makes a world of difference.
There's something else, too, but I can't place my finger on it. Is it the fact that the eye moves almost imperceptively about 24 times per second? That part of the eye is translucent? The use of the muscles around the eye? I don't know. It is a difficult thing, and even master painters often don't do well with the eyes. If you want believable characters, though, whether it is Spooner or the Hulk, ya gotta get the eyes right. Eyes and hands are the two most important features to know well, I believe.