My 12 y.o. daughter is discovering dystopian fiction, and this is her favourite book, EVER! Even better than the [b:The Hunger Games|2767052|The Hunger Games (The Hunger Games #1)|Suzanne Collins|http://d.gr-assets.com/books/1358275334s/2767052.jpg|2792775], she says. You just have to read this, mom! (In about four years from now, I'm going to introduce her to a whole other level of dystopian fiction and give her Atwood's [b:The Handmaid's Tale|38447|The Handmaid's Tale|Margaret Atwood|http://d.gr-assets.com/books/1294702760s/38447.jpg|1119185].)
This is perfectly and most squarely aimed at teenagers/YA. What better audience for a book about a society that is divided into like groups based on common traits? (It's kind of like the stratification that is happening in middle school). They adhere to strict societal controls based on their faction (those of Abnegation wear gray and try to be inconspicuous in all they say and do, and are excellent leaders because they are selfless, etc), and their coming-of-age means they have to choose which faction they will henceforth belong to. They must choose their identity, their grown-up self. They have to choose what kind of person they will be. And in the process they will learn about the complexities of human nature.
The book is strong in these themes of identity, the roles of citizens and society, and it also touches lightly on awakening romantic interests. The choices are strongly polarised, black and white, fitting in well with the strong sense of justice that this age group is developing. Wrap it up with some cartoonish smack-em-down violence, some teenage rebellion and revolution, and the ending is then set up nicely for #2 [b:Insurgent|11735983|Insurgent (Divergent, #2)|Veronica Roth|http://d.gr-assets.com/books/1325667729s/11735983.jpg|15524542].