As a non-Muslim, it's difficult to have an opinion about a book critical of Islam. Not only am I not a follower, it's not my native religion so I don't know very much about it. I am, however, a fan of Manji's work. So, I approached this book as her opinion about the religion and the culture and how they have affected her personally.
If you are already critical of religion – and specifically fundamentalists, authoritarians, and blind adherents – you will not find much new here. If you already know about the historic intellectual glory of Muslims, from art to architecture to the invention of our letters and numbers, you will probably already share her sadness that Islam's religious leaders seem to have turned away from the pursuit of new knowledge and instead seem to be trying to regress all of us into the past. Tracing the influence of colonialism on Islam may require a longer, more dispassionate, more serious work than this one.
Manji's tone is strong, and many readers have reacted negatively to it. She is young, and passionate, and I think it's important to remember that we criticize what we love. If she really hated Islam, she would walk away and never mention it again. Instead, she is trying to change it from within. It's a big task for one person to take on, and I think it takes a strong voice to make change. I'm looking forward to reading more from her.