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.
Another theme I would like to add which is linked to the other answer is the profound message that this important text gives us about the value of human life. Of course, the play presents us with a society that has sold itself to capitalism and the American Dream, yet the ultimate challenge of Willy Loman to such a society is his conclusion that twenty thousand dollars on balance is worth more than his existence. The text asks us some very hard questions that we are not able to ignore, such as can a man really be only valued at the amount of money he is worth? The disturbing suggestion of this text is that societies like America that have embraced capitalism wholeheartedly have as a by-product reduced human beings to mere commodities, with a resulting dehumanisation that we see in the character of Willy Loman.