3.5 stars, rounded up because Mayim is the bees knees.
I'm a middle aged guy with sons, not exactly the target audience for this book. Why did I read it? Well, honestly, primarily because I admire Mayim and was curious to read her writing. I also think it's a good thing for males to be aware of the challenges women face. With a few obvious exceptions, most of what Mayim writes about can also apply to adolescent/teen boys. It's certainly geared more towards preteen girls, but again, awareness is a good thing.
As to the writing, I admit I found it a bit simplistic for the young double-digit crowd. The writing seems geared more towards the very young adolescent - 10 years or so. However, it can certainly be argued that the simpler writing makes it more accessible to a wider audience.
Mayim's own world views certainly come through in the book (vegan, on the liberal side of many issues, etc.), but I also felt that she does a good job of balancing openness and respect for all cultures and viewpoints. Very conservative parents will probably not approve of this book, but that is their (and more sadly, their daughters') loss. The one pleasant surprise "exception" to her more liberal views is her discussion of modesty. It's an interesting stance and a brave choice for inclusion in the book. Kudos to her for her integrity.
Topic-wise, the book covers quite a range - biological changes, emotional changes, periods, reproduction, self-worth, body image, respect, charity, career paths, dating, love, intimacy, depression, therapy, boys staring at boobs (which she treats very gently, in my opinion), religion, friendship, etc. She handles all of these and more with a very straight forward style - just a caring adult wanting to share her experience, strength, and hope with girls and young women everywhere.