This is definitely my favorite book in the series. I really liked the characters (a genuinely ugly heroine! Woot! An emotionally stunted hero who's emotionally stunted for a real reason!) and the way their relationship developed. It was emotionally satisfying and I have a feeling I'll be rereading it one day. 
 Series review: 
 As for the whole four-book series, I have to say I'm disappointed. It's probably because it's multi-author, but the series feels disjointed. Book 2 is out of whack with the timeline of the rest of the series, and all in all, the series conclusion isn't very satisfying. Books 1-3 don't really have a conclusion because they end before The Big Bad is defeated, and the defeat of The Big Bad in book 4 is somewhat--how should I word this?--less than spectacular. You know it's going to happen. It happens. Meh. The awaited epic battle is less than epic. Or that's how it feels, anyway. (Did I expect more because I've had so much more in NS's Psy-Changeling and Guild Hunter series?)