I picked this up based on dozens of recommendations from friends and people on the internet, and it's one of the best YA Dystopian Novels I've ever read (and I've read a lot!).
Uglies, the first in a quartet of books, is set in a fairly distant future, after some cataclysm destroys the world in which we modern day people (referred to as Rusties in the book) live. The world is now split into many smaller cities, in which people are segregated according to their age: until you are 11, you are a "littlie" and live with your parents; from 12 to 15 you are an "ugly" and live in a dorm with other young teenagers; and from 16 onwards you are a "pretty" (new, middle, or late depending on your age) and live with other pretties.
The protagonist is Tally Youngblood, who has just lost her best friend because he turned 16 a few months before she did, and thus has already had the prettifying operation and been moved into New Pretty Town. Tally has been left behind in Uglyville, but she soon makes a new friend (Shay), who happens to have the exact same birthday as Tally. This initially fills both girls with excitement, as it means neither will be left behind. Or does it?
Shay runs away, and Tally has to choose whether or not to follow her. Her choice will change everything.
The book is, simply, fantastic. The characters are more interesting and three-dimensional than those in 90 % of other YA books I've read, and the discussions of what beauty is are rather breathtakingly deep. You'd think it would be very simple - an operation to make everyone look the same sounds horrifying! - but there are some fabulous arguments regarding the body image of Rusties that make it sound almost reasonable. There are also some very interesting themes regarding friendship, love, loyalty, and conformity.
Although this is the first book in a quartet, it works completely as a stand-alone - the end is open, but that's not necessarily a bad thing.
All in all, I would recommend this book to anyone who enjoys dystopian novels in any regard, and to anyone who ever thinks that the way we treat beauty in our society might be a bit messed up.