I REALLY, REALLY wanted to love Defy and it showed so much promise in the beginning, but this premise has been done before and done much better. Tamora Pierce's Song of the Lioness quartet was one of my favorite book series as a teen. Tamora Pierce's characterization, plot, intrigue, and romance were all spot on. But with Defy, there's a point in the story where the romance starts to eclipse everything else, and it all goes downhill from there. Way too much, "Which guy do I like more?" and not enough plot. 
 This is not one of those YA novels that can be enjoyed by adults in my opinion. I would say it would work better for the youngish teen crowd, but then there are some serious subjects in it, too, so I'm not sure who it would work for! For those looking for a well-crafted YA fantasy novel, I would recommend Pierce's series beginning with Alanna: The First Adventure, Rachel Hartman's Seraphina, or Sarah J. Maas' Throne of Glass series (suffer through Throne of Glass so you can get to Crown of Midnight because it's ah-mazing!).