In my opinion, Arthur Miller's Death of a Salesman is a tragedy. Willy Loman lives in an imaginary world, speaking to his dead brother, and forever feeling as if he has never measured up in life to his big brother. Willy has had an affair that his wife never learns about, but his son Biff does. This information alienates the two men.
Biff also feels like he is a disappointment, but that is because his father has never seen the value of who Biff is in being himself. Biff is always trying to be what his father wants him to be: an impossible task.
Willy needs a better job, especially because of the wear and tear his traveling does on the car and his long travel: he travels all day, sometimes for days. He speaks to his old boss's son who now runs the company. Instead of getting a job where Willy is closer to home, or even in an office, his "new" boss fires him. Willy is desolate. Biff is trying to tell his father that he is not what his father imagines him to be. Willy talks more and more to Ben, his dead brother, about what he should do.
Willy's difficult years and inability to face the reality of his own life and the lives of his family, have isolated him. Feeling that he cannot survive anymore, he takes his own life, even though his boys cared about him and his wife loved and encouraged him. No one grows as a person in this story; disappointment is a constant theme. I could not look at this play as anything other than a tragedy.