I hope that there are no spoilers in here. If there are feel free to put a Chainsword down my throat.
I will start by saying how much I loved this book. I have been disappointed with how the Horus Heresy has been going following Fulgrim. The first 5 were explosive and delivered everything that I wanted but for me they have got stale. I know many enjoyed Legion but I wasn't a fan, I really disliked Battle for the Abyss which just seemed to forget that Word Bearers were actually Space Marines not Imperial (Star Wars) Storm Troopers with very bad aim and I found the two Dark Angels books fairly pointless however we are most certainly back with a bang.
The First Heretic delivered everything a Horus Heresy book should. It answered questions but still left us wanting more. It made us care for both the heroes and the villains and it leads nicely into stories further on in the series.
The book follows the tragic Word Bearer captain Argel Tal who is coerced into playing a major part in the heresy while he tries to deal with turning on friends purely to pursue his enemies. While following his journey we see many important players in different lights, Magnus being the voice of reason, Guilliman as the enemy, Kor Phaeron as the father and Lorgar as the betrayed.
So what did I love about the book.
First off the scale of it. It takes place over hundreds of years and it still manages to move at a fast pace without skipping over huge pieces of information. The secrets and answers it delivers aren't in your face. On chatting about the book after finishing it my Dad and I both realised that we hadn't put two and two together about different things. Also we get to visit places that remain so important in 40k 10,000 years later and finally it features the Custodes and they are AWESOME. I was so angry when I finished Thousand Son's because it didn't portray the Custodes as I saw them, a step above Astartes and a step below Primarchs. Finally in First Heretic we saw them as the killing machines they are.
Of course it wasn't all good. Some of the combat was a little fragmented and the final face off was over far too quickly but they are minor issues. I really did love this book and I look forward to Aaron Dembski-Bowden's next work.