Oh Heaven! Absolutely brilliant. Not often do we have the pleasure of reading a sequel that outshines it's predecessor, but it is pure genius from cover to cover.
I can't figure out why this series isn't more popular, I would even go as far to say that I enjoyed it more so than The Hunger Games. The story flows and there are no awkward lulls I'm the action. If you love basic young adult end of the world type books, this series will keep you well entertained.