Scott Westerfeld invented an amazing dystopia with the introduction of Tally Youngblood. The characters in "The Uglies" were likeable and reasonably well developed without going into too much detail. "The Pretties" continued the saga with a story of overcoming obstacles and making choices for the greater good. "The Specials" was an interesting read but I was starting to get bored. Tally was no longer likeable but a person who had all the powers possible but she lacked an overall conscience until she started caring about the environment.
"The Extras" is part four in the trilogy (yes, I really did write that) and is exactly just an extra book. The protagonist is struggling with making sense out of the new world since Tally and her crew instituted free agency. The story takes on technology and those who are addicted to fame and sneaky ways of getting it (via FB, twitter, blogging, etc., although those programs are not listed).
Without including spoilers, I found the story to be interesting and relevant up to a point. The author has clearly developed the art of magnetic fields and how to use them to travel. I found myself having to skim that part of the book. I also didn't like Tally any better when she is introduced in this book than I did in the "Specials."
The ending left me dissatisfied and a little frustrated that I had spent the time to read a book only to find out that I didn't like the ending. It was an interesting take but seemed like a cop-out.