What is the theme of Death of a Salesman?

There are several themes to Miller's drama.  I think that
the most compelling of them is the critique of the American Dream.  The idea that
emerges throughout American History, and especially true in the 1950s, is that the
"American Dream" is defined by monetary success and the trappings of wealth.  The
natural connection was that emotional and domestic happiness will follow material
wealth.  Somehow, if individuals worked hard and made a great deal of money, they would
be happy.  In seeing the trials and difficulties of Willy, the reader understands that
this is not the case.  In this light, there is a strong grasp of how there are other
dimensions and components to achieving happiness in consciousness.  No matter how much
Willy works, there is a hollowness present, an emptiness that cannot be avoided.  What
Miller himself would term, "the matrix of his life," is one where the pursuit of
material wealth is unable to fully remedy the emotional pain that exists in his life. 
In this light, Miller's drama explores the fully complexity and richness in his
depiction of the American Dream.