My thoughts:
The valkyrie: GW wants to sell its new model. Having put the kit together today, also, I can say its a very nice kit and goes together very well. The thing is huge and will be a centerpiece for any army that fields it. The codex also clearly wants to help sell this new model. Its rules make it hands down the standout unit in the new codex. It has so much going for it, and for its points it is a steal - I will write up a tactica once I have a few games under it.
New units: There are sooooo many new units in the codex, its not even funny. There are a half dozen apocalypse tanks that can now be used in the game. There are also almost another half dozen speciliast artillery pieces or light tanks in the dex as well. There are new psykers and they are amazing. There is the new flyer. The guard got the royal treatment on models this time.
Power Level: We will have to see how this shakes out, but I dont think there is only a few builds out of the dex that will be competitive. There are so many options, I think we will see alot of variety on the tournament scene. The dex seems to be top tier, to me, as I read through it but we will have to see how things shake down.
The Fluff: The fluff in the book is light. The vast majority of the dex is rules, rules, and more rules. There is a little fluff at the beginning, but not as much as I woud like. However, I won't complain as the sheer amount of pages dedicated to the army and its units is amazing.
Rules: 4.5/5 (There are some ambiguous rules that need explaining with the valkyrie)
Quality: 5/5
Fluff: 3/5
Artwork: 5/5 (I love the pictures filled with guardsmen in the dex - they really evoke the grim dark feel)
Model Photos: 4/5 (I would have liked to see some conversions or new tank units)
Playability: 5/5
Power Level: 5/5
Overall: 4.5