I
appreciate that Aaron Dembski-Bowden is at least trying. While the dialogue, pacing, structure, and characterization of his novel The First Heretic are nothing to write home about, Dembski-Bowden at least understands what his job is in this novel about the traitorous Word Bearers -- it's to make us understand how falling to chaos is even possible, when its results are so obviously evil and ugly, and he does a commendable job at conveying the story. How someone goes from being pure to being utterly corrupted is interesting fodder for a story, and it needs to be handled with some reasonable amount of skill and planning. Graham McNeill completely flubbed this, both playing down Horus's goodness in the begining of False Gods, and completely rushing his turn to the Gods of Chaos in a highly unbelievable way.
By contrast, Dembski-Bowden illustrates the fall of the Word Bearers by first placing them on the unsteady pedastel of "faith" (naively written, but effective enough for the plot) -- the Word Bearers are pure and good, but a bit misguided and nostalgic. They are then publically humiliated for an action they believed to be righteous, and their loyalties are pushed to the brink. Their primarch Lorgar's pride is played upon by the forces of chaos, and while the exact reasonings that go on are a bit melodramatic, there is a sympathetic through-line to the actions of the Word Bearers and their leader; such that by the time they start making deals with demons, you can understand how they got there.
This is the interesting part of moral failure -- understanding how someone could take the path that leads to atrocity, while still utterly rejecting the actions they end up taking. I still think that the themes can be taken on by a defter hand than Dembski-Bowden's, but I do commend him for his vision.