For £45 for the standard edition, it is a hefty investment. For your money you get two full codex-sized books, one full of story-developing fluff, the other a comprehensive supplement to Codex: Chaos Space Marines. Whilst this book does work on its own, you need the old chaos book for tanks and other units, as the new book only covers the shiny new models.
First the fluff. And without wanting to spoil anything, I will say it is fantastic story development, and the Space Wolves sure do get a good kicking. Magnus, the first ever daemon primarch to grace the 40k game (not epic!), is made out as the ultimate schemer, barring his chosen deity. He's also no slouch on the battlefield, at one point (SPOILER ALERT)
...takes an orbital bombardment without so much as a broken bone. It's very rare you get a demi-god like this, and now he has rules (yaaay!).
And speaking of rules, if you're you're a fan of low model, high powered units, this is your army. Sadly the Thousand Sons didn't go down in points, but for the first time the basic squads have options, as well as new army units. Mini guns, flamers, beastmen and the Scarab Occult, we now have new units and rules to go with them.
On first impressions this army will dominate the psychic phase. From generating changes on a 3+ to ‘irresistible force’ powers, there are several formations and artifacts which means you can throw out a ton of sparks and flames. As well as this, all sorcerers have and success to a far superior tzeentch discipline, as well as access to all the major disciplines for higher ranked sorcerers.
If you want to add to your Thousand Sons or start an army of these guys, this book is essential. If you just want the rules, the chaos legions book is out and features the sons plus the other main baddies, but the fluff in this book is too good to miss.
Next time I'll be analysing the units and giving an example of a list I'll be trying next, as well as well as preview of the new units I've added.