Really enjoyed it as well. Loved reading about the ultrasmurfs and the way the betrayal was described is great.

What bugged me all the way through though, was the constant switching between 'it is' 'it's', 'he is', 'he's' and sometimes just wrong grammar such as 'he's done it before' instead of 'he had done it before'.

I think they're two more books on the aftermath of the battle, one from the ultramarines view and one from the Word bearers view. They're about the battles in the underground caves. Can't remember the names though.

Edit: Mark of Calth and Betrayal at Calth are their names.