The series is in my opinion an achievement, and it should be taking into account that it is very hard to continue writing on characters established by other writers. This haveing been said, Book 5 is still by far the worse of the 6 books, despite the incredible events that do happen in this book. Like other reviewers said, the characters are suddently behaving in unexpected ways. When reading book 6, one can understand why (the team of all writers together I assume) this was felt necessary for the storyline - but Athans does a very poor job in bringing this about. It looks like most characters are suddently devoid of any depth (apart from the one who never had any!)I was also not happy with the actual writing style. In addition, there are two inconsistencies (or at least those I identified) with the previous books, and it felt like the author couldn't be bothered to read all 4 books in detail before completing his.
I was determined to find out what happens it the end, so despite my frustration at points I did finish it and Book 6 rewarded me. Don;t let the reviews stop you from completing the series, it is worth the time to read all books and the conclusion is brilliant.