I'm going to say this straight up; if you want this book to make a shapeshifter, make a druid or a hunter instead. No, seriously, your party will thank you.
The Shifter is hobbled from the moment it gets Wild Shape, an ability you would expect it to excel at. They are limited to forms that match the Aspects they know, which means that at level 20 you will have 5 available animal forms to change into. THAT'S NOT A TYPO. For comparison, druids, in addition to their 9th level spells, have 0 limitations on what they can change into, whereas the class built around the concept of changing shapes can't manage more than 5 at their peak. Hunters with the Feral Hunter archetype always apply their Focus and can shape into any animal. The reason I mention their Focus always being on, is that the Shifter is not so fortunate. Their Aspects are 3+level minutes per day, and like the Hunter the physical boosters are enhancements, so they need to be turned on to keep up with the other martial characters.
The archetypes for the Shifter have some interesting concepts, but are generally of NPC-quality stock (some have ridiculously low per day usages) and need some errata already.
As for the rest of the book, it's your standard Paizo fare of useful and useless feats, a wide variety of archetypes for the other (better) classes, and more rules about the minutia of nature and the wilderness than a DM could dare dream of.
