Well Chase, this book is going to get me back into 40k for 6th edition.
The costs of champions went down considerably, which if you always fielded them in a squad, makes the new squads seem cheaper. The almost universal access to marks makes fielding a mono god list less punishing and more acceptable. Using the icon system for buffs instead of just marks removes the annoyance most people had in the 4th edition codex.
Except for a couple odd FAQ issues, like the zombies and their options, I think the book will prove to be a nice change to the 4th edition chaos codex.