I am a huge fan of these '32k' style books. really enjoying the Heresy series, it is my favourite 30/40k event. But seeing the aftermath is fascinating. most 40k books involving traitor legions are pretty much just them as gribbly worshippers, evil, because they are evil. I loved the Night Lords trilogy and the detail paid to their struggles for basic materiel, crew etc. Whilst we enver really had much Heresy fluff, there was almost nothing for the period after that beyond the Primarchs being killed or vanishing. finding out more about all the legions immediately after the heresy can only be a good thing.