I've always kind of liked the Beast-Bonded Witch archetype for it's ability to give your familiar feats instead of taking one yourself, and while there are a lot of cool feats to give familiars same as players, this book introduces new familiar ONLY feats that can really flesh out a beast-bonded witch's familar!
As to the rest of the book, don't expect a Bestiary of Animal Companions and Familiars... that's not what this is. If you expect, that you will be disappointed.
No, this is a small little book to help you make more fun familiars and animal companions. With the new familar/animal only feats, new archetypes for animal loving characters (rather cool is the "Carnivalist" rogue who is like a carnival animal trainer who is able to train his animals to be rogues along side him somewhat (they can pick locks or steal for you, or even sneak attack!)) but also adds new tricks for all trainers. Plus... ANIMAL ARCHETYPES! Now not every cat famiiar is the same, your cat can specialize as an "Infiltrator" and gain things like Uncanny Dodge instead of speak with it's kind. Your faithful hound can be a valet which allows him to use prestidigitation, aid you, and even gains all teamwork feats you have.
I must say, as a player of arcane casters (and even my sorcerers I find a way to get a familiar be it bloodline, archetype, or feat) this overall is very much a must have book for me!
Some of the Pathfinder staff once said (and I agreed) that one of the problems with 3.5 was there were TONS of prestige classes (if I recall correctly, the word "bloat" was used), and that this was something they wanted to avoid with Pathfinder. When they made a prestige class, it would have meaning to the campaign setting. So, we got one or two maybe three here and there, but not a large amount of prestige classes... until now. But, this book does NOT in my opinion make a mistake. Every class in this book is based on a faction or other such part of the Pathfinder Campaign Setting (Golarion) that makes it so players won't just be looking at the prestige class for the powers it can give them, but for the fun and flavor of the character.
Some definite gems from my initial reads of the PDF before my hardcopy arrives and I can curl up on my couch for more serious reading (and this first one... I'd love to play on in a PFS game!) are the Snake Oil Sales... I mean Razmiran Priests. Yes, these powerful arca... I mean divine spellcasters can heal you by the power of The Living God, Razmir! Sure, those are only temporary hit points. But it's ok, because by the time they wear off you'll likely either be dead from additional damage or have healed enough naturally that you won't notice, so let's all bow to Razmir, The Living God!
Then we have the Grey Gardeners. Galt's executioners who, at level 10 learn the secret ritual to extract a soul from a final blade (and even before that, can draw a soul into their sword and then later stick it into a final blade.)
There is also the Shieldmarshals, which are Alkenstar's guards and investigators both protecting the people of Alkenstar and helping to enforce Alkenstar's monopoly on the gun trade, along with many more prestige classes that all fit in and enhance Golarion as a setting.
So, while not every class will be useful to every player and every campaign, all of the classes have meaning to the campaign setting far beyond just a collection of cool abilities. Even just seeing the names of the classes, I can tell what faction or aspect of Golarion they represent.
So, while I do not own the 3.5 Pathfinder Campaign Setting, I've had chance to read through it. I purchased this new version from Amazon, and I must say the new book is far superior. The setup of pages is nicer, the material is more in depth, and I really didn't notice anything "missing" that I felt was mandatory from the original. The updates to the prestige classes kept the flavor but also made them more in tune with the Pathfinder rules changes. Also, I very much like that the Harrowing spell is detailed alongside the Harrower prestige class for those that don't have the Harrow Deck (which I do, but still)
Overall, I wholeheartedly recommend this book to anyone who likes the Golarion setting, even if I did own the 3.5 book myself, I would not feel bad to have purchased this new version.
About the only complaint I have though is that the Hermean Blood feat doesn't tell you anything about Hermea or where to find info on the region, nor does the index. I had to fully read nearly all of the regional description sections (Something I would have done eventually, just not in the sitting I Was looking at feats and was like "What is Hermea?") before I found it. A reference to the page # Hermea is on might be nice in an update for future printings.