I'm pretty happy with it overall.
Rules:
The OP stuff is, in fact, pretty OP. Fortunately, it's pretty easy to avoid taking wraith knights and scatter bikers (the only two really problematic units I've spotted so far). 5% of the units became too powerful, and the other 95% got some flavorful boosts that won't break the game. There's nothing I'd find impossible to field now.
The formations are all really neat, but the detachments all require over a hundred dollars worth of models I don't have, so I probably won't get to benefit from the said detachment much. There's some controversy at my local store over whether or not I'm able to field the formations without taking the detachment. Any thoughts?
Fluff:
I've read a lot of it before, but I appreciate what's there. I could read a whole novel about each of the craftworlds, but finding out about things like the Morai-Heg's handmaidens or the lost Shining Spears Phoenix Lord (whom I will be statting up shortly) are fantastic. The little stories sprinkled throughout and the fluff tied to the runes and color schemes is very cool, though most of the runes being variations on "Kurnous this," and "strike unexpectedly that" gets a *bit* old. I feel like the harlequin book had more fluff to it, even just regarding the various factions, but I like what we got here. Still, it could have used more elaboration. Something like the Kabal of the Poisoned Tongue's raid timeline from the dark eldar book.
Photo Galley:
Not a huge fan of these. In the dark eldar one, there was at least a bit of cool captioning sprinkled through the images. These are very well done images that inspire me to get an army together, but so are a lot of the images I can pull up on a Google search.
Formatting:
I'm really glad to see each unit type getting its own page for fluff again. Still having fluff with the unit entries is nice, but giving full pages to the seers, various aspects, etc. is much appreciated. Things are relatively easy to find in this format, and I suspect that will help as I start to get games in.
Overall, a pretty good buy that will probably get more hate than it deserves. Play responsibly, folks.