This volume is not as extensive as any of the preceeding volumes and seems a bit more of an afterthought (or easter egg even) than the others. That's not to say that is isn't well considered or written: it is. It just doesn't do as much justice to the material as Slaanesh or Nurgle does.
Commencing with a discourse on the Ever-Chosen, the book descends rapidly in to an un-targeted review of the pantheons of the races of the Warhammer world. I think Tzeentch could have done this in a much more (shall we say) "insidious" manner. Its not that the material doesn't fit, but I just wonder if it should have been shuffled elsewhere and with a different "accent"?
The volume is rounded out with an essay on the "unaligned powers" (but where is Malal? ha!) that aligns well with material from the Lost and the Damned and terminates with Be'lakor.
Given the brevity of the volume, this one is the weakest of the series -- it could have been made much better. More could have been made of it through greater exploration of the nature of chaos (perhaps even shifting the ideas of souls given in the Tzeentch volume to here) and giving greater emphasis to the independents rather than the Warhammer pantheons. A brief vision of even Horus could (nay: should!) have also been added, let alone the Black Legion.