The design of the Pathfinder system leans heavily towards feat driven characters. Most classes receive twice as many feats as their 3.5 counterparts. These feats are used to design more dynamic characters without the use of PDFs. Logic would state that the more feats you have access to with this system, the more diverse characters you can create.
Bad puns aside, the UndeFeatable series by LPJ Design expands on the feat selections of Pathfinder classes. Each entry highlights a specific class and introduces a little over a dozen new feats. UndeFeatable 4: Barbarians not only presents feats useful for the class, but creates a new selection of Barbarian feats that adds some creative flavor to our wild raging buddies.
Barbarians are famous for their raging ability, so it is to no surprise that UndeFeatable 4 either enhances are uses rage in all but one of the feats it lists. The feats are descriptively written, allowing barbarians to gain more rage powers as they slaughter foes or as they take wounds. .
Those feats are good, but the really impressive ones are the Aspects, groups of feats that instill animal traits onto your barbarian. More than just an enhancement of the rage ability, aspect feats allow the barbarians to take on stat traits and abilities of various animals. It is very reminiscent of the old totem prestige class but a bit more dynamic in terms of control.
For the Player
Aspect Feats can really bring the background of your tribe into play.
For the Dungeon Master
I can imagine there are a great deal of ideas to establish undocumented regions in your campaign world by using villages made up of barbarians with different aspects.
The Iron Word
UnDefeatable 4: Barbarians continues the solid series of UnDefeatable books by providing classes options without painting a template onto them. The feats are nice and the Aspects will provide some new paths for the Barbarian.