Kick a** ending.
The ending was the best part for me.
I love the new Tally. Being the last special Special, I loved how she makes use of it. She and David will be the New smoke nemesis. David and Tally will be the ones to stand in the way of anyone who tries to destroy nature. I really think it's cool.
This book was the perfect ending to the uglies series. I liked that Scott westerfeld didn't end it as a happily ever after story where the new smoke was free to do whatever they want (which will then eventually turn them to rusties and the whole cycle begins again).
The next thing to do now is to read Extras.