If you take Barbarian at level 1 then you get the option of taking one of two background traits unique to barbarians: Tribal Barbarian and Totem Barbarian. Each feat unlocks regular feats that can only be taken on Barbarian levels and improve the Barbarian rage in a variety of ways. See the feats for more details on them and the feats they give access to.
Additionally, Thundering Rage, available to all Barbarians as an improvement.
Improved Uncanny Dodge now grants full immunity to sneak attacks.
Generally speaking, since many of the new feats scale with Barbarian levels, and only work when rage is active, then it makes sense to go pure or almost pure Barbarian. However, some interesting options could exist with Tribal Barbarian/Bard and Terrifying Rage, since the DC of that is affected by Intimidate, so one could make a kind of Viking Skald type character.