Disclaimer: I like nature based characters so this review may be a tad biased.
For those wanting a more down to earth upbringing traits abound with the core races each getting one & it includes a way to add some partial fey alternate racial options to each as well.
Witches get a lot of love here with 5 new patron options, a new Hex & a flavorful archetype. An herbalist system was touched upon that works great with this new archetype.
The Rogue has several thematic talents added that while a couple could be useful they seem mostly flavor. The same can be said about the inquisitior & alchemist archetype.
The Summoner got an archetype that seems interesting. Have yet to incorporate it in game but it definitely has potential.
The Shaman was also shown some attention with a new spirit (its always nice to get more options with the newer classes)
Many of the feats introduced are situational at best.
The main draw here (aside from the witchyness) are the traps, items & tools of survival. Normally I tend to gloss over 1/2 of the items introduced but everything here served an obvious purpose.
The information in this book is worth the buy, especially if you are a Witch, Rogue or Trapper.
The description of Unchained hardly does it justice, this thing is brimming with tweaks & "hacks" that put so much more balance into the core game its staggering.
For better or worse all the classes from the 4 taking center stage (Rogue, Barbarian, Monk, Summoner) in the opening chapter to entire subsystems that bring the Fighter up in a much needed way (stamina), Several varrying magic systems that can slightly nerf spell casters so those in melee feel less useless (limited magic, wild magic, fumble magic, esoteric materials), several ways to simplify play (simplified spellcasting, spell attack rolls, alternative skill systems, alternative alignment) every class can be touched or tweaked in some way to bring things more in line with fewer balance issues overall.
Best part aside from the Summoner (if you play pathfinder society) it is all optional!
Even many ideas that I saw as less than ideal were presented in a way that can be used to streamline so many things, especially from a GM standpoint. The monster creation system is Amazing! For players the variant multi-classing is much easier to contend with than current level dipping to qualify for prestigie classes.
Sure a few hiccups occasionally sneak in that can be nit picked about (many monk archetypes are invalid, ki pool no longer a rogue option, severely limited Eidolon) but as a whole I am so glad I got this, it turned a weeks worth of game planning down to a day or 2, helped one of my less than stellar mathematicions get the Barbarian concept they wanted without constant questions being addressed mid battle & made skills & spells less if a pain to explain to the new girl.