My review is for the series as a whole. Uglies is the story of a dystopian future. All people go through surgeries at 16 to become pretties - before that they are called uglies, and live apart in special dorms. Tally Youngblood is an ugly on the eve of her 16th birthday. The trilogy tells her story, as she finds a group of people who have not gone through the operation.
Uglies is fairly compelling. I liked tally, and I was interested in her story. The world itself seems pretty poorly realized, as is often the case for dystopia. Maybe I'm being strange, but I really like to see books with economies that make sense. The world of uglies doesn't seem to have an economy - other than a few doctors and scientists, most pretties seem to party all the time.
In the second book (warning, spoilers!) we spend a lot of time in pretty town. Unfortunately, the author chooses to have the pretties use a really horrid form of slang. Yes, I know why, but if I had to hear something called "bubbly" one more time...
My recommendation is that the first book in decent, but the others squander all that promise. And since the first book ends on a cliffhanger you will want to continue. Don't - it is so not worth it.