I know no novel is perfect. What flaws are there in Steinbeck's novel The Grapes of Wrath?

It's a good call to understand that all works have some
imperfections.  Having said that, I think that it's hard to find flaws with the work of
Steinbeck.  So much of it is exemplary that to find challenges within it is a
challenge.  I think that a fair critique though lies within how much faith and primacy
he places on social activism and solidarity amongst others.  Steinbeck's ending is one
where individuals rise to the moment and unify in the face of overwhelming challenges. 
Tom stands up for Casy's ideas, Rose of Sharon becomes a sacrificial figure, Ma's
lessons about honor and solidarity are enhanced.  Steinbeck views consciousness as a
social experience.  The other side of this coin might be true, as well.  Individuals
might simply wish to be left alone or seek to advance their own sense of self and not
identify with a larger contingent.  Steinbeck emphasizes the idea that social solidarity
is a part of human consciousness.  One might wish this to be the case, but the reality
is that people do turn away from one another and either seek to be left alone or look
after their own interests.  This is not something that is present in the thematic
development of the novel, as it squarely argues that human consciousness is a
collectivized and unionized experience.  If there is a flaw in the work, it might in
this configuration of human nature.