I should start this review by saying that this product impressed me by offering content that touches on unfilled design space that I've never thought of before. This is very rare and great to see. I definitely want to see more books in this vein in the future.
Onto specifics...
Animal Companion/Familiar Magic Item Slot Allotments by Body Type
This is awesome and something that the system has needed for long time. I'm not going to say that the whole thing is balanced (because it's not) but the fact that this is broken down in an easy to use simple format is a great resource for a standardized format like PFS.
Archetypes - Carnivalist (Rogue), Huntermaster (Cavalier), and Mad Dog (Barbarian)
These are all great thematically and mechanically.
One major nitpick is the Mad Dog's Ferocious Fetch ability which allows him to command his animal companion to use the Drag manuever as a Swift action. Commanding an animal companion is already a Free action. Pay attention to these things editors.
Animal Tricks
The expanded options here are great and some really surprised and impressed me. Bombard, Aid, and Flank I'm looking at you. Never again will hard-nosed DMs be able to claim that your wolf/bear/koala isn't clever enough to step into a flank for you.
Feats
There's nothing really inspiring here but I love the precedent set here. There are feats in this chapter designed for familiars and animal companions to take - with their feat slots. I'm especially impressed that the text makes mention of the fact that familiars can pick up these feats by trading out feats they come with by default (very smart).
Animal Archetypes
Again, I love the prescedent set with this section and it's something I've never considered myself.
Again, a nitpick.
One archetype gives an animal companion ridden by a cavalier a bonus when charging. This replaces Share Spells.
Designers/Editors, Please Read
New Companions
Panda, Llama, Walrus, Moose.
NO LARGE BEAR