Satisfying conclusion to the trilogy, with plenty of little twists and turns to keep the reader guessing but ultimately gratifying. Still plenty of space for a continuation of the series, too, should the author decide to try it (or space for the reader to let her imagination run free, should she feel so inclined). 
 My impression of the trilogy overall: 
 A little hokey, honestly (I mean, the entire thing revolves around a princess with a magical gemstone in her belly button for heaven's sake), but super fun anyway if the reader can just get over it. Reminded me of Tamora Pierce's Alanna stories -- a little bit ridiculous if you've gotten used to more nuanced "grown up" fantasy, but really good all the same and definitely the kind of thing that could get a young girl (or boy!) into the fantasy genre in the first place. 
 That said -- and I'm not the only one who's noticed this -- Carson could have used a way more thorough editor for this series! I try to be forgiving because, hey, mistakes happen, and the story is strong enough to draw me in anyway, but all the little mistakes really started to add up! 
 Actually, I found myself wishing that the books were done as a full-fledged adult series rather than a YA trilogy. Glowing belly jewels aside, I think the story and the world it's built in could easily have been expanded (and in some ways refined) into multiple 800-page volumes... but maybe that's just me.