I bought The First Heretic (TFH) at Games Day and read it on the coach back. It's a strong performance and I'd rate it as one of the best of the Horus Heresy books to date. In places I would rate it as equal to or above Horus Rising. In his blog, Mr ABD makes a reference to the difficulty of topping Dan Abnett's introduction of Horus. In my opinion, the confrontation between Lorgar, Gulliman and the Emperor is easily on a par, possibly exceeding it for emotional impact. There is also another scene towards the book that also hits the very heights of what we have come to expect from the best writers in the Black Library stable.
Unfortunately, due to the scene mentioned above and the constraints of writing a HH novel that has to cover specific events in the canon, the book does feel as though it peaks early. There is also the nature of Lorgar himself as a character to consider. ABD does an excellent job of portraying him as essentially the most tormented and flawed of the Primarchs (but consequently perhaps the most human?). This is necessary, given that it's Lorgar's need to find a divine spirit that will accept his adulation that ultimately triggers the Horus Heresy, as though he were the flaw in an otherwise perfect crystal that when hit at the right place, causes the whole construction to shatter.
As a result of this characterisation, the book fails to exalt the Word Bearers in the same way that Soul Hunter did for the Night Lords. By this I mean they lack a certain WOW factor. Personally I've always felt that the more Satanic nature of the Word Bearers should spill over to their Primarch in some way and I was left feeling a little disappointed, given Lorgar's general lack of bad arsery. However, again even if this was an angle the author wished to pursue, that particular niche has already been taken by Horus (whose fall has the theme of pride, twinning him with Lucifer).
I predict that Mr ABD will find himself the target of those who will accuse him of favouritism. Not wanting to give spoilers in a review, let's just say that the Night Lords nearly steal the show at one point. I don't think this is nessarily valid criticism, as they are used in a way to reinforce the author's main themes. But at the same time, I don't think that this was what the general audience was looking for in a book about the Word Bearers, possibly as it violates a major staple of 40K fiction: take the group that will be the protagonists and make them AWESOME (as done by good effect in Soul Hunter, Titanicus and Brothers of the Snake). Again, it's worth noting that this approach would have jarred unpleasantly with the fact that in this book, the protagonists ruin a shining beacon of light for humanity to satisfy their own inadequecies and superhuman immaturity.
The combat is a bit inconsistent. One of the major battle scenes failed to ignite my interest, but others definitely grabbed it.
In my mind the "Dark" trilogy by Anthony Reynolds still reigns supreme as "The Book of Lorgar" for Word Bearer fans. TFH's focus is telling the events that shape the galaxy, the Imperium and the Legion, but I doubt it will inspire many to collect a Word Bearer army. However, it does paint an excellent picture of their origins, the source of their hatred and provides us with a beautiful depiction of the possessed, their state of mind(s) and the transformations they undergo.
In short, I'd say that it deserves four bolter shells out of five, possibly dropping to a solid 3-3.5 if you're a die hard Word Bearer fan. It again proves that Mr ABD has the technical skills to be one of the leading lights of the Black Library, but constrained by the task of having to add flesh to the framework of the Horus Heresy, I got the impression that he couldn't bring his full talents to bear. Bring on Blood Reaver say I!