What I love the most about this story is the numerous unexpected twists. Almost every chapter ends with a cliffhanger that made me want to keep reading.
The story is told in multiple POVs, clearly delimited by sections within each chapter. I normally prefer a single POV, or alternating between two characters, but this complex story couldn't have been told as well with only one or two POVs. We see the thoughts and actions alternating between the two main characters, Charlotte and Elderfield, as well as those of some minor characters: a warrior elf, a druid assassin, and even Siren himself, sprinkled throughout the story.
I love the voice in this novel. Charlotte is a modern, human girl from England, and I just really like her thoughts and expressions. This, of course, contrasts with Elderfeld, a teenage elf from another realm, who doesn't always understand what she's saying. He gets a chance to visit her realm, and finds it fascinating, although he does get in "a bit of bother" during his short stay.
There was a bit of violence at times, mainly with creatures such as trolls and terrorhawks. There is a war raging, so of course, there has to be some more intense scenes. This would greatly appeal to most boys, and it didn't bother me, but it might be a bit too much for more sensitive readers.
(reviewed the day of purchase)