There were a lot of things I liked about this book, but also a few things I didn't like.
1. The Fantasy Element - I was impressed with the djinn folklore that was used as the basis of the story. It seemed well researched and was used intelligently, and I liked the references to literature such as The Arabian Nights, and the New Oxford Book of Verse (My daughter now wants to check out those books :)
2. Strong Protagonists - John and Philippa are strong, smart children who show quick thinking, teamwork, and problem solving skills.
3. Humorous Supporting Characters - genial Uncle Nimrod, xenophobic Mr. Groanin, and wise, meek Mr. Rakshasas made me smile.
1. The Pacing - UGH, in the first half of the book almost *nothing* happens! Lots of talking, lots of instruction about djinn history and what they are. I felt like I was reading my daughter a mythology article. The last third of the book, the action picks up and it gets more enjoyable.
2. The Writing - I won't say that the writing was all bad, but some of the dialog was a bit stilted and not particularly realistic for the 12 year old siblings. It helped to read it out loud with a child's tone of voice, but it just wasn't quite right. Some of the paragraphs were a bit convoluted and it was tough to get the right phrasing the first time when reading aloud.
Overall I enjoyed the book. I hope that some of my complaints are a symptom of this being the first book in the series with exposition being a necessary evil. My 10 year old daughter really enjoyed it (in fact, when she read my review, she told me that she completely disagreed with my criticism) so we will be giving the second book a chance.