That's a real shame...Have yet to read Angel Exterminatus but one of my fav Legions and Primarchs...and all they get is a cameo in Battle of Phall where they look like incompetent fools (even with the attack lead by the Perturabo!). I think this Primarch needs at least a novella to open him up. Other Primarchs got so much more attention!
Hey hopefully you like it, I actually wish the best for the Heresy Series. There were certain aspects of him that seemed interesting. Yet, this is post Istvaan and Phall and he seemed like a completely different character.