The only reason this gets a 4 and not a 5 is because it is an interview. Think of this as a survey class for all of Campbell’s other work.
For those who do not know the impact of Campbell–beyond the rather well known fact that Lucas consulted him for Star Wars– his concept of the Hero’s Journey is taught by most creative writing teachers, almost as if it were gospel.
This is a rather simplistic way of viewing fiction and oversimplifies Campbell’s teachings. I recommend his other books, if you can find them. Many are out of print and most are not light reading.