Once I finished Book 1 of the series I was hooked and immediately bought Book 2: False Gods, at around midnight on a weeknight. As with Horus Rising, the first line is a heck of a hook: "I was there the day that Horus fell..."
While Horus Rising really didn't show much of how the heresy took root other than threats and hints, this novel quickly dives into the emerging divisions within the Legions. The story centers around the events on the world and moons of Davin. Horus is tricked into leading his legion to the moon which has been overrun by the influence of Nurgle.
Once again, I enjoyed the balance between action and intrigue, embodied in part by the division in points of view of the human and Astartes characters. One of my favorite parts was when Loken is portrayed from the human point of view and the incident in question shows the fine line the Astartes walk between good and evil action.
My one major complaint from the novel was the way in which the heresy took root in Horus's mind. Several parts of the story are told from his point of view, including the period of enchantment/fever dream that leads to him turning his back on the Emperor. The problem I had was that the decision seemed contrary to his internal monologues that preceded it. He sees through the lies and enchantment being forced upon him, but still ends up siding with the side he knew was lying to him. While I don't think he should have been duped into turning against the Emperor (at least not by human manipulation), his change in reasoning shifted to the point where I couldn't follow it. Perhaps a rereading will reveal something I missed.
Continuing from the first book, there is still enough hope to make the tragedy of what we know is coming sting, but also plenty of foreboding and apprehension for the characters. Among it all are some nice little hints and teasers about things that are not directly addressed. My favorite was hints of what could have happened to the two "lost" Primarchs, as well as an interesting question of if Horus was being given visions or actually being taken back in time to see the Primarchs cast into the Warp by the forces of Chaos. He has a real effect on the world he is shown, and the Emperor recognizes him.
The book ends with a similar seed of doubt as was included at the end of Horus Rising, which serves as enough of a cliffhanger to get me to immediately download the next book.