Late to the party but I broadly agree with what si said here. I really feel the IH just come across dull in the telling. Maybe it is inevitable, take the human weak flesh out of the already a bit cut out Astartes and they get less interesting. ADB is a freaking genius (as is Abnet for me, though i know others argue) because the endows the astartes with personality and drive. Pythos sucked because not only did we have the not so interesting IH, but we also had an enemy who was just a bunch of monsters with little personality themselves.
I think Annandale did a fairly mediocre job but I think the deck was stacked against him. What about the IH has actually been good so far? Abnet did a great job in extracting character from the cookie cutter ultrasmurfs as ADB did from the potentially cookie cutter Night Lords, and McNeil did a rare star turn with the richer material of the TS, but the IH plus the author with a bit less weight really made this a dull book I am afraid. I got through it only as I was on a plane. Reading it after Talon of Horus was also a mistake, as that was so goddam good i was even more disappointed. I also tried to read death of Antagonis, but found that equally bland and bailed.