Betrayal is the first book in forgeworlds new line of Horus Heresy based army books. I use the term army book in the loosest sense in this regard because it makes up only about 1/3rd of the actual book.
The first impressions of this book are quite frankly jaw dropping, it's a reassuringly weighty tome, with a textured leather cover, metallic corners stamped with imperial eagles and silvered page edges. Frankly it looks good before you have even opened the cover.
When you do open the cover, you are treated to a full colour interior with detailed background on the events leading up to the heresy, composition of space marine legions and resources, not to mention the full colour pictures of models produced by forgeworld.
Although I haven't read the entire book yet, the sections that I have read do not seem to be plagued by the same startlingly obvious errors typically seen in a forge world book. So hopefully that means that quality control and proof reading haven't been overlooked in this book.
Within the book you can find rules for some of the characters featured in the early black library novels. As well as the rules for fielding Primarchs. More specifically rules for Horus, Angron, Mortarion and Fulgrim.
So how do the primarchs stack up against regular warhammer models then?
From my impressions it seems as though forgeworld have managed to make the Primarchs actually playable in a game of 40K. While these guys cost as much as a death star unit, they are a death star in their own right. Able to go toe to toe with most things you could encounter in a game. Horus himself is a beast hitting like a railgun in close combat with plenty of other bonuses available to him. Each primarch is differentiated from the others in cost stats and wargear, also in the bonuses they bring to their warriors.
While £70 is a lot of money for a book I would consider this a worthwhile purchase to anyone who is a fan of the Horus Heresy or just the forgeworld books in general.