When a director undertakes a film presentation of a popular novel or play, he has the right to infuse his own interpretations of its theme and character. This is certainly true of Death of a Salesman by Arthur Miller and its movie counterpart starring Dustin Hoffman and directed by Volker Schlondorff. While the play stays true to the script, Schlondorff took some liberties in other areas.
First, he deviates from Millers copious stage directions in which one set is used for multiple scenes. Miller spends a page and a half describing his set, clearly indicating his vision for holding to Aristotle's unity of place. However, scenes with Biff and Happy as children, the other woman, and even Ben, are far more detailed and presented as one would expect in a film, very realistically. This detracts from Miller's style of creating dream-type flashbacks occuring only in the mind of Willy. Stylistic deviations aside, this does tend to make the viewer better able to understand these sections of the play.
Second, the character of Willy, noted to be large and like a "walrus" in the play is cast using Dustin Hoffman. The words describing Willy's size are changed to conform to Hoffman's small stature. This loses the full effect of Willy's downfall. He is more devastated to have lost his intimidating image in the play. This element of physical demise is lost, leaving only his emotional demise in the film.
Finally, the play focuses more on Willy's illusion that being well-liked is all that one needs to succeed in the business world. Willy's inability to reconcile this belief with the changes in business practices are central to the play. In the film, more focus is put on Willy's insanity and less on his inner conflict. What used to work for him as a salesman, no longer does. As a result, the film version lacks a clear connection between the failures of Willy and Biff, an important characteristic in the play.