Second book in the series of the Dark Angels background, Fallen Angels tries to deliver the reasoning behind Luther's threachery on Caliban (home planet of the chapter).
Continues directly after the events of Descent of Angels, so shares some characters, some are new, and the warhammer futuristic setting is depicted perfectly, only exagerating a bit the resistance of the space marines (but not too much either)...
The pacing of the story is much better in this second book: Two parallel main characters and associated stories in different places (one in the Dark Angels' homeworld, the other in a planet with Horus rebels). Pretty well told, keeping interest even when part of the ending is known, and even with small twists (nothing great but good enough to serve their purpose).
I didnt liked the "humanization" of Nemiel's team, talking as typical cocky marines. Being space marines they are supposed to be badasses without the need of mocking typical movie bluffs and semi-jokes. It kind of disrupts the non-talkative, 200% war focused adeptus astartes image.
But this is a personal taste, other books keep this semi-humanization of Space Marines so whenever I like it or not, I have to bear with it.
The book is the nexus with what will become the "hidden" current Dark Angels secret, unfolding how it happens and what happens but not how it ends (yet, that's what the third book is about). But this time, and unlike what I felt with the first book, what is told forms a whole and is correctly both delimited and depicted.
Now we're talking about real space marines adventures.