Realistic in the sense that Spiegelman doesn't make his dad out to be this perfect man who survived the Holocaust but a man complete with many flaws - and maybe more flawed because of his experiences.
Spiegelman depicts his father and all Jews as mice. The Germans as cats and the Poles as pigs. The Swedish are some kind of deer or elk, and the Americans are dogs. Often times the mice wear the mask of another nationality.
Spiegelman's series is a good one to share with teens who are interested in the Holocaust as they are graphic novels. They contain some language and adult situations. In Maus II, Spiegelman delves into his own mental health issues from being born to parents who survived the death camps and lost their first son in the Holocaust. These are quick reads, but pay attention to the pictures as much is depicted there.