Somebody has probably already posted on this book, but I love it so much! I just finished it, and I loved UGLIES (book 1 in the series) almost as much.
Westerfield has created a future world, where you are divided by how you look. When you are young (a.k.a. 'Littlie') you live with your parents in 'Middle pretty Town'. (Ignore the crappy city names!) When you are twelve, though, you are sent to 'Uglyville' (again with the stupid names,). There you are raised by computers, fed, clothed, and taught by a hole in the wall. You are also taught to think of yourself as a hideous creature who can't wait to turn 16.
Once you are 16 you are sent to an operation. An operation where they sand off your face, smash all your bones, and then make you look beautiful. Pretty. You look like everyone else in 'New Pretty Town', sweet, innocent, and vulnerable. And gorgeous.
In this new world, killing animals and trees was considered barbaric. You instead used metal.
All Tally ever wanted was to be a Pretty. She was always tricking the technology, to sneak into New Pretty Town to watch the partying and fun going on with the pretties. (Did I mention that that was all Pretties had to do? Have fun?) But then she is told what terrible things that the operation can do to you, and she changes her mind a bit about turning 'Pretty'.
I can't tell about Book 2, without giving away Book 1!
Go. Read. It.