I love this series because starting each book I think, "Oh yeah, THIS is my favorite in the quartet!" It just gets better with each one. This book does a great job both ramping up the stakes and showing the growth and maturation of each character. My only complaint is Alex - I assume the author was leaving his motivations unsaid because she felt they were obvious, but on each reread I'm left unsatisfied. Was he magicked by Roger? Is he just a sociopath? Why is he ok with the complete destruction of the kingdom? My end conclusion is usually that for whatever reason, his entire purpose in life was to prove he was the best, all else be damned, and maybe there's a scene on the cutting room floor that better explained it all.
Overall though, very satisfying wrap to the series and one I'll never tire of rereading. Already looking forward to coming back to it in a couple years!