In the general realm of Warhammer 40k books, this is fairly high on the quality scale. It's not overly info-dumpy, it his back on the people per, and it achieved a good mix of action and plot movement.

I'd have liked some more warp grotesquery and grim darkness, actually, but as the backbone of the Horus Heresy this book does a good job of driving home the bitterness of betrayal.