I've only read The City of Ember and have started People of Sparks, and I have no intention to stop.
In the first book--City of Ember--a young girl and a young boy with big dreams bond once more over a common interest, and the girl displays her skills in physical attributes, while the boy shows his own skills academically. The two combine their skills to solve a major problem, and the book covers the struggles of friendships as two people mature and go in different directions, when betrayal occurs, and when secrets lie buried beneath the surface of all that seems true. The book was very well executed, and I definitely recommend it to children, teenagers, and adults.
The second book, People of Sparks, is so far displaying how tough it is to choose between a friend who helped everyone around her, and the cool kids who can make dreams come true...or make them crumble in an instant. The harsh reality of life is pressuring every character in the book, and as the children of Ember become teenagers, peer pressure is taking hold. I'll give the book a final review when finished.