The Gatsby section goes back to the early days of the revolution, and chronicles the heady times of ideals and the gradual encroachment of the values of the Islamic Republic, culminating in a rather funny court scene where The Great Gatsby itself is put on trial. Nafisi is pretty merciless in mocking the intellectual contributions of the most doctrinaire of the students, and I suspect that they are an easy target.
The second half of the book chronicles her gradual disengagement from Iran and eventual emigration. It's still very good but the first half is the essential part of the argument, the bit that Marjane Satrapi doesn't have as much of.
Wikipedia has an account of the criticism levelled at the book and the author from various quarters. A lot of it simply isn't fair: Nafisi is a specialist in English-language literature, so it's hardly surprising that she chose that as the subject of her classes. It is true that of course this may play to the prejudices of the monoglot Anglophone philistine, but this is clearly not Nafisi's purpose. Another rather peculiar criticism is that the book describes Iran at its darkest, between 1979 and 1996, and things are better now. This is unfair because Nafisi is diligent at specifying dates, to moor the narrative to a particular set of points in the past rather than the present, and at portraying a society as it changes for the worse, but at the same time showing hope that it may change for the better. (And anyway, while things may have improved slightly under the later presidencies of Khatami and Ahmedinejad, I don't get the impression that the improvement is much to write books about.)
Part of this, of course, is a reflection in Wikipedia of the peculiar toxicity attached to Iran in American public discourse. I was utterly astonished the other day to catch a CNN commentator describe President Ahmadinejad as the most evil person in the world (I do not paraphrase). There are a lot of other candidates; most of them are of course on better terms with the US government. The concentration on Ahmadinejad as hate figure (consider also the extraordinarily inhospitable remarks made by the President of Columbia University when introducing him back in September 2007) also displays an unwillingness to get to grips with the roles of the Supreme Leader and Council of Guardians. It is a shame if Nafisi's book helps perpetuate those prejudices, though I can't believe that a thoughtful reader would take that message from it.