After reading Persepolis 2 I have come to the conclusion that while it is another excellent book from Marjane Satrapi, it doesn't hold quite the power of Persepolis. I suppose it couldn't. Persepolis focuses on the life of Marjane in Iran when she was 10 to 14 and when the Islamic Revolution was just beginning.
Persepolis 2 begins just after the ending of Persepolis. Marjane has gone abroad to live in Austria. It shows Marjane adapting to a life which is more free but not necessarily any more satisfying. But after four years in Austria, having a freedom that her friends back home could barely imagine, she decides that she has to return to Iran, that the life she has isn't necessarily better than the oppression in Iran.
These are two very good books, but the Return doesn't have quite the power of her childhood in Iran. Both are worth reading.
Persepolis showed me that the graphic novel can be much more than a comic book with super heroes and violence and action. It can tell a much more personal story. I do realize that there have been graphic novels before Persepolis which have done this and that Persepolis is only part of a tradition, but it was my introduction to the tradition.