The Grapes of Wrath created an insane stir when it came out. People were furious. They thought John Steinbeck made the whole thing up. They refused to believe that migrant workers were really living in such terrible conditions.
But sometimes the truth is stranger than fiction... even when it's then fictionalized. Steinbeck did his homework, and the novel portrayed a hellishly real set of circumstances. Today, it serves as a time capsule—as well as a massive word of warning.
But this isn't just a book that chronicles an era. Its also a pretty timeless quest saga (how timeless? it's still being taught in high school, to give you one massive example). The Joads seem to undergo an odyssey for peace and happiness. While it is arguable as to whether they ever achieve this peace, the novel vividly details the quest and all of the gruesome obstacles that pop up along the way.