Why bother with literary background for a film? Well, it's a good starting point. While I can't vouch for the adaptation's quality, I can vouch for the film's quality. It's a really good film and if you haven't seen it, it's something you should definitely check out.
Set during the Depression, The Grapes of Wrath settles on Tom Joad (Henry Fonda), a recently released convict. After serving four years in prison for manslaughter, Tom returns to his family home in Oklahoma. Tom's return isn't what he expected; it's in the middle of the dust bowl and his family is gone. According to his neighbor, Muley Graves (John Qualen), Tom's family moved to California in search of a better life.
After catching up with his family at his uncle's house, Tom joins his family on the long trek to California. The trip is rough, but the family's dream manages to keep them in good spirits.
In a very rough sense, you could look at The Grapes of Wrath as a "road trip" movie. Most of the plot details the family's trip West, though the focus is clearly on Tom. It's an interesting personal journey, taking him from a family-centered loner to someone who looks out for everyone. It's a familiar tale, but one worth retelling over and over again.
Part of the magic is due to Henry Fonda's acting. He's perfect as the main character and helps build up a true "Everyman" persona. It's a great bit of acting, but also compliment's John Ford's tone perfectly. The underlying message can sometimes jump up and smack you in the face, but overall it's communicated clearly and with a great nod towards the reality of the situation.
The main feature is joined by a surprisingly deep set of extras. First up is commentary by scholars Joseph McBride and Susan Shillinglaw. Each has their own focus (one the filmmaker, the other the author) and the two mesh nicely. There's just as much here for the film buff as there is for the literary nut.
Next is a short biography of producer Darryl F. Zanuck from A&E. This 45-minute presentation is great, but then again you'd expect that from an A&E documentary. Though it doesn't exclusively focus on The Grapes of Wrath, it features outtakes from the production as well as other Zanuck productions. There's also a series of interviews and other archival features. The main focus is his rise in Hollywood, though it also delves into his personal life when appropriate.
Next is a set of Movietone News reels from 1934 that set-up the film's setting as well as one of Roosevelt praising the film industry. If that's not enough, there's also the U.K. Prologue, a set of text screens introducing the film's backstory to non-U.S. audiences.
Finally, there's a short gallery detailing the restoration process the film underwent.
While I don't see myself checking out the novel anytime soon (sorry every English teacher I've ever had), I really enjoyed the film and can't recommend it enough.