As a book, this was well-written with a good plot. As the final book in the series, it left me unsatisfied. While there is a lot of things to pack in a small package, this book felt rushed. The ending was predictable, but somehow unsatisfying because everything was quickly wrapped up in the last two chapters. Nice, quick pace for young readers, but still left me wanting more out of it.
Having said that, I do plan on reading the companion books, because I think this is a very good series.
This final book is more graphic than the first three, with a few scenes that made me a little squeamish (Dragon scene, Mulgarath's fate). I can see my 6-year-old self being very upset with these scenes, so keep in mind for young sensitive readers.
Overall a good book.