First of all, it took me longer to finish a Darren Shan book than usual because the book is bigger in size and has more pages.
This is a review about the book The Thin Executioner:
The story is more about beliefs, slaves, myths...so as many reviewers before me said, it's not a book you expect from Darren Shan, but that doesn't mean its not a good book. The book is very interesting, set in ancient times where people believe in slaves and gods.
The writing style in this book is very different than all Darren Shan's previous books. The narrating is in third person point of view rather than first person point of view. It takes a while to get used to this narrating change, but you get used to it.
I personally loved this book although it was difficult for me in the beginning to get used to it. Although you're not used to it, you still want to find out more about what happens. The characters are well-developed and likeable.

Don't expect the same vampire/demon style that Darren Shan writes here. Although I should say that a change is great. We should see different ideas from any author. Anyway, I recommend this book to all Darren Shan fans; don't be disappointed, and don't give up reading it halfway through.