Dark Vengeance is the second book based on a GW boardgame or WH40k edition I read (first was Space Hulk novel), and as a spoiler, again I feel it is a weak read made just to complement the 6th edition box set.
We're told the story of how the Dark Angels, who on their (typical) search for the Fallen hit a planet where they find not only chaos cultists, but renegade space marines from the Crimson Slaughter chapter and the battle they get into. Each chapter is told from different points of view, not only from the loyal marines, but also from chaos ones and even weirder subjects as a cultist or even the hellbrute. This makes some chapters feel... strange, culminating with the librarian being able to see far in the future some stuff by fraction of seconds (pretty much like recent Sherlock Holmes movies). Add to that that half of the story is pretty bland and typical, and yes, we indeed learn the origins of the new chapter of chaos space marines but... I felt dissapointed, I just expected something less dumb. Also, not entering into details it didn't felt to me as "the mind" of a chaos SM* would think and work that way.
I haven't read other books featuring the chaotic space marines so might be how they are portaited, but if so... I'd rather keep my imagination flowing.
Overall, a dull reading, you can skip it.