It's very interesting. Since I'm braindead I'm going to copy and paste a review.
It is easy to look at this book and think, "Oh cute! Bunnies! This looks like a nice story to read to my five-year-old!" What you are getting when you pick up this book is much different than what the cover tells you. Heather and Picket are plunged into the broken world outside of there sheltered lives. Natalia (their world) is a war zone filled with distrust and betrayal. But, it is also filled with courage and hope in the 'Mended Wood' (the mending of their broken world). This book is filled with beauty, battle, hope, courage, loyalty, and everything else that is needed to craft the perfect series for kids (and adults!) of all ages. S.D. Smith is comparable to C.S. Lewis, J.R.R. Tolkien, and many other masters in his writing style and beliefs. He is truly one of the masters of our age.
Do be cautious, though! While this first book is certainly not as intense as the later books in this series, they do have a fair amount of action and adventure. Do not pick this book up unless you want an action-filled read!
Also, this first book gives information away slowly, but don't let that stop you from reading the rest of the series. The next few books move MUCH quicker.
A lot of people on the forums have read, and loved the Green Ember series, and I think you would too!