I'll be honest, I have no idea what the idea is behind WotC-era barbarians. Some sort of mystic nature warrior who isn't the ranger mystic-nature-warrior?
My idea for a barbarian is based on Howard's Conan: physically and mentally tough, able to endure what would break a softer, more civilized man. So here's my concept of the barbarian for my TSR-era, mostly B/X mashup:
Barbarian
The Barbarian hails from a distant and uncivilized land. They are ignorant of the ways of magic and the manners of the glittering courts of civilized nations. However, their rough and rude upbringing grants them exceptional hardiness and endurance.
Requirements
Barbarians roll d8 for their hit points. However, they start at 1st level with 16 hit points.
They may use any armor, shields, and weapons.
Barbarians save as Dwarves.
A Barbarian must have a STR of at least 9 and a CON of at least 13. If a Barbarian has at least 15 in both, they enjoy a 5% bonus to all earned EXP. If they also have a DEX of at least 13, that bonus goes up to 10%.
Abilities
A group that includes at least one Barbarian is surprised only on a roll of 1 on a 1d8.
Barbarians enjoy Advantage on saving throws against illusions and only suffer a -1 when attacking foes who are invisible or otherwise can’t be seen.
When resting, a Barbarian adds half their level to the hit points they regain (minimum of 1).
When a Barbarian deals a foe a killing blow, they may immediately make another attack on a target that is within 5’.
When a Barbarian’s melee attack roll totals 20 or more, they may perform a Feat of Arms. This can be things like moving an enemy 5’, disarming their foe, hurling their target into another foe, etc. Be creative!
Barbarians are expert climbers and hunters. For every 4 hours they spend foraging or hunting, they produce 1d4 rations. Environment can heavily influence this, however.
Brian’s Notes
Conan was my model here. You’re hard to take down, so if you want to be a living brick wall, this is the class for you. You probably won’t be performing Feats of Arms quite as often as a Fighter, but you’ll still enjoy this class more if you enjoy coming up with cool things on the spur of the moment.
Illustration made with Stable Diffusion and GIMP.