Bonds of Vengeance seems to serve as the bridge between the first two books in the series in the last two. Having just finished this book I can't say for sure, but I can say that this book tidies up a lot of plotlines from the first two while still leaving a couple major ones to be addressed, and...
I found Shapers of Darkness to be the weakest of the five but I can't quite place why. The pace moves along rather quickly but I found myself thoroughly uninterested in certain plot lines (most predominantly the goings on in Galdasten)--so much that I took a nearly three month hiatus from reading...