This may be a book for younger readers (I found this book in the Children's section of the library), but I really like Shanon Hale as a writer, so....
This book is really enjoyable. At first, I thought it was bildunsroman, but it turned out to be more of a mystery story then anything. The main character, Elodie, can be a bit annoying at times. Actually, she was fairly annoying in the first few chapters, although I don't know why, but she grew on me, and I by the end of the book, I was rooting for her.
This book has a slew of characters, from an ogre to a handsome cat-trainer. But apart from Elodie and the dragon (the detective, which is really cool), and maybe the ogre, but I felt that the characterisation was not very well done. Most of the characters started falling into stereotypes (e.g. The Ditsy Princess). But I will say that the stereotyping was partially successful, since it was used for a dramatic twist.
For this weird, random reason, I was reminded of Jane Austen. I read once about Emma, that Jane Austen plants hints about what happen, so that on the second reading, you will notice all the hints. A Tale of Two Cities was a little like that. When I was thinking of the book, I could see a few subtle hints weaved into the text. However, it's a little lacking, especially when it comes to the White Schelpur (not too sure about the spelling, but it refers to a person who appears kind but is really evil inside).
I'd actually recommend this book to people of all ages, especially younger kids (from upper primary upwards, although a precocious child could probably read this sooner), and people that don't like reading. Because this story combines mystery and bildunsroman with elements of fantasy, it can really capture the attention of the reader.