I am on the final stretch of the book and I am still reading the adventure.
The problem I have with the book is that it's the weakest of the series.
I found that the Tome of Fate and Tome of Blood were the strongest. While Tome of Excess suffered from a strong editorial revisionist hand.
Tome of Decay suffers from what I can best describe as being two books mashed together into one - Nurgle and Chaos undivided (with ascension tacked on). Nurgle is described in brief overview. Unaligned powers are described in brief as well. Abaddon the Despoiler is given a text box. Both of which demand the player to go to third party sites to learn more.
The adventure on Mire is a good example of combining a plague world and apotheosis into one. It's a nonsensical adventure to run with a group that are not all Champions of Nurgle. The encounters have no why except to fill time. The construction of the adventure appears to be haphazard as well, the stakes and motivation of the adventure are scattered in the text and not actually covered in the GM overview.
I will finish the book before I give a stronger verdict, but I felt it to be over all a weak yet cramped book.
-C