I'm really not sure where the author was going with this book.
Sometime in the future, in a post-apocalyptic dystopian world, thanks to government/societal mandate, children grow up, hit a birthday and are shipped off to have mandatory radical plastic surgery so that everyone can be a "pretty." Apparently, looking different (or not pretty, according to whatever parameters have been set by the future rulers of society) is what has caused all of the problems in the world.
We have Tally (our protag?) and Shay, who are both "Uglies" (those that are too young and have not been surgically "enhanced" yet) as the two main characters. Tally is yearning for Pretty life, because her best friend "Peris" aged out and was made Pretty and lives with the other Pretties. Shay meets Tally and becomes her new BFF and questions the conformity of it all.
Apparently, the progression goes Pretty ("New Pretty" actually), Middle-Pretty (middle age) and Old Pretty ("Crumblies). Uglies are young and in school, they play pranks and general act out and are kids. New Pretties are mindless celeb types who just party all of the time and don't seem to have any sort of responsibilities. Middle Pretties seem to be the work force, they've now been enchaned so they show their ages but are still "Pretty", they have the jobs and the kids (Littlies, who seem to live with their parents until about 12). Crumblies are the geriatrics, and I'm not exactly sure what they're up to - the book doesn't go into them as much.
So anyway, The story covers mostly Shay and Tally, two uglies who escape and find an outside-the-city encampment of those who have rejected the conforming way of life and are trying to encourage and gather others that are not so keen on the government rule. They use and try to recreate old technologies (from the "Rusties", who are presumably based on our society, which has fallen) to supplement their way of life, so we hear a bit about that as well (and the environmental destruction that caused the fall of civilization as we know it). The bad-gov't guys are trying to find people and keep them in line. Along the way, we have a love triangle, so Shay and Tally can cat fight about a guy, because that's what girls do.
There are plenty of themes through the book, but none of them are very strong. Westerfeld seems to be going along with a "government dictatorships/conformity/beauty standards" are bad, but doesn't really go there all that strongly. More like he is using that idea to help fuel the story, which is otherwise fairly weak, imo. The characterization isn't strong, but I wouldn't expect it to be for a book that seems to be about messages, but the messages and plot aren't that strong either.
I'm not sure where the series is going, but I'm pretty sure I won't be reading any more of the trilogy.
It was merely Ok for me.