Because nobody wants to post it, I am more or less summarizing the discussion in efu-main.
Problems:
-- AoE fear without an action; therefore it can't be clarity'd
-- Is it too strong? Does it last too long? Is the DC too high?
-- Regardless of strength, is it too common? Is it the bard equivalent of a healing song?
-- The effect isn't affected by Spellcraft or PfA.
Solutions:
-- A "breath before the shout" that emotes a warning before the fear effect takes place next round.
-- Adjust intimidation contribution to DC or amount of rounds the effect lasts
-- idk the rest I sort of stopped listening
Considerations:
-- Powerful multiclasses get access to wands of tasha's, hold person, and dispel.
-- The instant action mechanic of the rage only effects the 5% of the playerbase that have the wherewithal to drink Clarity as someone is using a wand.
-- DC 15 fear effect is more or less the floor of a level 8 barbarian.
-- Are the other furors too weak if this one is being constantly used?
It's only overpowered in my view at the moment because of all the problems you have listed but it could easily be tweaked to be balanced. The DC potential at the moment is too high given that it does not seem to factor in PfA and spellcraft etc. The fact you can activate it instantly is extremely strong as it is pretty much war cry (spell) on a stick and just to correct the above post, you can multi-class as a barbarian and still have access to wands etc and this furor.
So the tweaks could be allows PfA (vs barbarians alignment) to work and spellcraft.
OR
Change the way the DC works to DC:10 + Barb Level - Multiclass Levels. (Reduce DC by 1 if Intimidate is less than 2x class level for each 2 intimidate). Also just get rid of the -1 will no save as that seems unnecessary.
It's a very powerful capability for barbarians to have, and I'm somewhat OK with it. I'd maybe just recommend that the availability of the fear furor be a little more rare.
I think it's perfectly fine, it needs to be an action, not something that can be done instantly.
Given how easy it is to stack intimidate on a barbarian, maybe it's scaling should be adjusted.
It definitely feels too good right now. Barbarians are already a solid PvP class, they don't really need an "Save-or-loose" button on top of that. And let's not forget that even if the fear save is passed, the debuff to attack and damage is still potent (Bards take Curse Song for a reason after all).
While all the nerfs above would work on a pure power level fix, my favored fix would be to reduce the duration of the fear (not the debuff) to 2 rounds. It makes the furor less about having an instant win button and more about taking the tempo. You have 2 rounds to attack the target, putting them on the backfoot, but they can still turn it around. It becomes a strong advantage instead of just auto-loose if you fail the save.
Make it +1 DC / 4 (or 5) Intimidate instead of 3.
Make the Fear also effect nearby allies/neutral PCs.
While I know there'd be faction issues, make it so that it only effects friendly/neutral/enemy PCs and only enemy NPCs.
I'd just like to chime in and say that there should be a delay to the actual fear effect going off.
It is a bit crazy that barbarians get a fear shout that can be activated instantly at the press of a button with a relatively high DC and as a FREE ACTION.
Have them emote that they are taking a deep breath upon entering a rage-like state.
If a 1 or 2 round delay to this "save or loose" mechanic was added that'd already solve any and all balance issues. Literally.
One round is a long enough delay. Any longer poses a threat of being too weak.