One reason I can think of to read this novel is that it is a story of survival. The author is writing about his childhood, which is dysfunctional and one of extreme poverty and deprivation, yet it has a lot of lighthearted humor to it and, most importantly, the author survives his difficult childhood, alcoholic father, disease, death, poverty, etc. There is no bitterness in the story, no self-righteous judgment. Frank McCourt refused to become a victim, in spite of all the hardships he faced growing up in Ireland. In spite of all the people that tried to knock him down and keep him down, he eventually rose up out of the ashes and made something of his life. He was also able to become a caring teacher because of the sufferings in his own life.
I think this novel shows the resiliency of the human spirit and that people can choose not to be victims, but to be survivors.