The Lost and the Damned by Guy Haley

Better than the HH average fare. The principal characters and threads being brought to a head helps make up for the usual bolter porn.

I do worry though that some the central conflicts are given short shrift with no hint of further clarity:
[Primarchs] “Why didn't daddy tell us about Chaos.”
[Malcador] “Chaos is awful, daddy knows best.”
[Primarchs] “That's true.”