Portraits are a very special form of photography. Because it is by far more personal than any other form of photography. There is only a very thin line between bad and good portraits. A good portrait reveals something of the true character and personality of a person. Sometimes in a beautiful way, sometimes in a charismatic way but always in a respectful way.
In order to achieve this a photographer must establish a positive (and trustworthy connection) between himself and the other person. All this shows in the portrait. A bad portrait on the other hand only reflects the surface of a person.