Beyond your expectations.
I disagree with the other reviews on this stating that there is too much violence. It's nothing more than what you would see on Saturday Morning Cartoons if it were described in words. While I am an older reader (23 - I know, what business do I have reading a YA novel? All Business, that's what.....and yes, I watch Saturday Morning cartoons...) I truly think this book would benefit the YA audience. We want to branch out and show our kids how the world is by skimming just the top. That's this book. (No, I'm not suggesting your child will fight a giant crab or have a back-stabbing friend that can remove it's limbs and head....)
The writing style is different from "Fablehaven", it has basically evolved. While I liked "Fablehaven", this was an overall exciting page turner that I did not want to put down and did not want it to end.
I truly loved the new races of characters added to this book, particularly Jasher's race that has a sort of spiritual/worldly significance. I also loved the displacers. I truly think they will have much more of an impact in the next book, but they are a race that is because that's what they are perceived to be.
I'm 'getting used' to main characters with both a male and female lead role, and this one works out very well. I usually prefer one or the other, but not in this case (:
Every word is carefully crafted and propels you into it's broken world of old coupled evil wizardry. Again, our Assistant Pig-Keeper is called on upon to perform tasks we are woefully unprepared for. ( "The Prydain Chronicles" - Lloyd Alexander.) [No, I'm not saying Jason/Rachel are Assistant Pig Keepers, yet they do resemble the lovable Taran.] And Who doesn't love normal-seeming protagonists destined to a duty he/she never thought himself/herself capable of? And yet, this book is truly a stand-a-lone. Brilliant. Absolutely brilliant, Mr. Mull.
I cannot wait for the next release.