No doubt Grapes of Wrath was a very fine novel, which is precisely why it took me so long to understand what I have come to regard as the profound intellectual swindle that was going on. I, too, would recommend it be read if only as a masterpiece of composition.
It will take too long for this venue to explain why I ended up feeling like I'd been manipulated by Steinbeck, but briefly here it is: the actual events surrounding the Dust Bowl involved a sense of community and sacrifice, and perhaps even heroism, on the part of the community banks Steinbeck vilified, many of which went under with their communities and took bankers and farms with them through no fault of the personnel of either. The upshot of the novel (and the later movie) was an emphasis on greed on the part of a faceless, evil group referred to variously as "the banks" or "the owners" in the novel, personified unfairly and, I think, far too useful to demonize a generation of people in the economy whose sin was failure in the face of an irresistable environmental and economic force, not venality. It was also extremely exploitable for those who insisted that capitalism itself was a root evil, and has remained so.
I don't blame Steinbeck for the attitude, and I do applaud him for his articulation and his skill as a novelist. He deserved the Pulitzer and the later Nobel, this novel being largely responsible for the latter for reasons that I have always suspected revolved its utility to anti-capitalists. And maybe it's purely personal, but I've always blamed this novel for casting my own attitudes in a mold it took a decade to break. It was a very big book with big ideas, and it had a very big effect on me...which was how I interpreted the question, and why I gave that answer.