Favorite - Fulgrim, Thousand Sons, Nemesis. Fulgrim was such a complete book and so well written. Goes to show you how Dan Abnett has influenced the other 40k writers and how far he has pushed them to do better. I am a long time 1k player so how could I not love A Thousand Sons. My only qualm is that not enough was said about the trial of Nikea, like how Magnus left before the Emperor and how that was completely out of character for any of his sons. And I liked Nemesis because it showed the players behind the scenes and how far Malcador is actually willing to go to.
Least Favorite - Prospero Burns. This is the only book in the series that I couldn't read. Flash backs; Dreams; False Memories; not getting to Prospero till the end of the book...yeah no thanks. Very surprising that Abnett dropped the ball on this one so spectacularly.