I agree with Daniel on this.
To me really great portraits aren't the over retouched glam pictures that seem to dominate but the portraits that are real and honest. The ones that when loved ones and friends look at the portrait they say to the photographer that is so and so. The portraits by Arnold Newman, Marc Hauser. Irving Penn, Walker Evans, Richard Avedon's American West portraits, August Sander, etc.
A few words by some of the greats
"I think photography is a matter of controlling what’s in front of you and making it do your will. This, of course, implies absolute mastery over camera, medium, techniques, and the ability to work with the subject and get him willingly and happily without any self-conscious feeling to fall into those things which are natural to him. This is a very complicated thing to do in portraiture. Mine are deliberately self-conscious portraits and therefore contain no forced feeling of candidness… the subject is unaware of the fact that I am waiting – things begin to happen – the man begins to reveal himself.” “If the background becomes overwhelming and you lose the personality, then I have not made a good portrait and it is not a good picture. I think the world is full of intelligent people who are not really trying to be flattered; what they really want is to be understood”. “The more I get to know my subject the more he gets to know me, and so often the pictures taken at the end of a sitting are much better both creatively and interpretively… A photographer is always in a state of preparing himself for a given moment… we have only an instant in which to think and act."
Arnold Newman
"Pure photography allows us to create portraits which render their subjects with absolute truth… if we can create portraits of subjects that are true, we thereby in effect create a mirror of the times."
August Sander
"When a portrait evokes a feeling, then you’ve got something. Technique isn’t really important. What I want is a believable moment."
Bert Stern
"It’s one thing to make a picture of what a person looks like, it’s another thing to make a portrait of who they are."
Paul Caponigro
"It is one thing to photograph people. It is another to make others care about them by revealing the core of their humanness."
Paul Strand
"Nothing is more hateful to me than photography coated with gimmicks, poses, and false effects. Therefore let me speak the truth in all honesty about our age and the people of our age."
August Sander
"It seems dangerous to be a portrait artist who does commissions for clients because everyone wants to be flattered, so they pose in such a way that there’s nothing left of truth."
Henri Cartier-Bresson