Oh! Didn't know how it worked, then- it's confusingly worded. That said, auto-crits are something people can combo with really, really well. At minimum, you take one attack which you might not have instead (0.3-6 attacks worth, depending) in exchange for turning an attack which hits into a crit (x2 damage = +1 effective attacks, x3 = +2 attacks, x4 = +3 effective attacks).

Alright, overall thoughts:
It's a much better Barbarian, with some stuff which makes it somewhat better (not great) against outsiders. If this is your first homebrew, it might be easier to take the parts you really care about (outsider sensing, hatred, possibly the diehard thing), and turning them into a Barbarian archetype. It would make it much easier to balance as a result- you assume the Barbarian is balanced, pick some things to take away from it, and give it things which look approximately equal. I think you could make the following swaps with the basic Barbarian safely:

Fast Movement is traded for the endurance feat and the ability to sense evil/good outsiders within 60 ft (i.e. the Brand)
Uncanny Dodge is traded for the diehard feat
Trap Sense is traded for an equal bonus to attack and damage rolls against outsiders.
Improved Uncanny Dodge downgraded to Uncanny Dodge

If you want to add armor use, I would trade Fast Movement for armor proficiency (medium),
Uncanny Dodge is traded for Armor Proficiency(heavy) plus the ability to sense outsiders within 60 ft
Trap Sense is traded for an equal bonus to attack and damage vs. outsiders
Improved uncanny Dodge is traded for Endurance and the Diehard feat.