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.