When I read the first book, I remember hearing that Lu had originally planned to re-write the Les Miserables story as a YA dystopia, and someone had suggested she change the gender of one of the main characters, allowing a romance to develop. So June is effectively the Javert character and Day is Valjean in the first book, Legend. Lu does a masterful job of contrasting philosophical positions on the best ways to run a dysfunctional society that has been decimated by war and plague - where geographical boundaries have been moved around and it's difficult to know who to trust. The two leads become unlikely allies and move on to the second part of their adventure in the second book.
I was prepared for Prodigy to be a let-down as it didn't have the skeleton of the Victor Hugo classic to give it shape. I was pleasantly surprised that I liked it possibly more than the first book. The characters' struggles are deeper in the second book and their alliances are tested almost to breaking point. The ending also seriously brought tears to my eyes. Both books have a lovely sense of closure although it's clear at the end of each that there are more issues to be resolved for the characters and their world, so plenty of space for the next book in line (but without making the reader feel like the author has left us hanging!)
I've said it before and I'll say it again, but one thing that separates a good book from a really great book is the development of the secondary characters. When the secondary characters are more than just props, but are real people whose issues shadow and contrast those of the main players, bringing their struggles into sharper relief, you have the makings of a really special story. And Lu is a master of making all her characters ring true and each of them contribute to the story in his or her own way. So for me the thing that makes this series a standout is not just that it's a clever dystopia with an unusual genesis, but the characters are so strong that they feel almost like real people that I can care about, down to the lowliest of minor players. I can't wait to read Champion.