Willie doesn't make it based on Aristotle's guidelines. Willie is not a "noble" character with some obvious "greatness." That being said, this is where Miller would argue that our nobility and greatness does not depend on our position in society, but upon our basic humanity. Miller writes, "I believe that the common man is as apt a subject for tragedy in its highest sense as kings were. On the face of it this ought to be obvious in the light of modern psychiatry, which bases its analysis upon classific formulations, such as the Oedipus and Orestes complexes, for instance, which were enacted by royal beings, but which apply to everyone in similar emotional situations."
There has always been an argument about the nature of tragedy vs. the nature of pathos. I have always felt that Willie is a character that instills pity and fear. After all, who are we to think we are inherently better than Willie, and who of us might not be destroyed by our dreams as Willie was ....
You might want to read Millers "Tragedy and the Common Man." You can find it at http://vccslitonline.cc.va.us/tragedy/milleressay.htm
1. High status/noble virtue--I would say that Willy thinks he fits this category; he sees himself as a rather well-liked salesman. There may be people on his route that will always buy from him, but it doesn't necessarily mean he is of high status.
2. S/he is not perfect. Willy does fit into this category; Willy is basically an Everyman, the Average Joe and many people can relate to his struggles, making him not fit in category one.
3. Character flaw/error in judgement--Willy definitely fits here. He thinks the secret to success in life is being well-liked and can't deal with his own failures, so he puts pressure on his sons. His inability to be happy with what he has and allow himself to be proud of his work and his sons is what leads to his suicide.
4. The punishment exceeds the crime. Willy is not necessarily punished--it's self inflicted, but most readers would say his reaction/punishment was overdone.
5. The tragic hero learns something before s/he is punished. This isn't true in Willy's case or he wouldn't have killed himself.
6. The tragedy doesn't leave the audience in a state of depression. DOAS has a depressing ending. In the requiem, there seems to be little hope.
Based on the above, I wouldn't call Willy a tragic hero.