First of all, I want to say amazing work on this latest version! It is my favorite so far and thank you to all involved (this is more or less the only game i've played for like 10 years). I also love the new extreme barbarians. In the past I looked for mods that would make barbarians more threatening but even Barbarians Evolved and Barbarian Immersion didn't boost them much. But I think with a few tweaks a few aspects can be improved. For reference, I play Marathon speed, Huge map, 14 civs, Immortal, Raging Barbs, Unique City States, More Promotions.
Wishes with respect to barbarians and game pacing:
I really like the idea that barbarians are an existential threat to the player. They shouldn't be able to wipe out a player, but they should make it extremely difficult to accomplish anything. Specifically, the settling of your second city should be a herculean task that requires all the concerted focus of citizens and military. I think for gameplay (and realism too?) that you should be more or less cowering behind your walls focusing on defense until you build a significant military with an upgrade or two. Once you establish a foothold/perimeter of 3 adjacent cities, then it should become easier to defend yourself and field an army large enough to both defend against barbarians and begin looking for conquest opportunities. But even at this point, I think escorting a civilian across a continent should be suspenseful. Not all successful diasporas required a massive military, but barbarians have to represent ALL the challenges of a 3 year walk through untouched wilderness, like disease, animals, etc. that aren't currently represented in the game.
Don't wants:
*I don't want barbarians to be a chore to deal with... the currently CONSTANT spawning is a bit too much.
*I don't want barbarians to be such an 'opportunity' for players... a barbarian encampment should be somewhat concerning, not seen as "Hooray! 100 free culture!". And even for aztecs and askia, barbarians shouldn't just be an all you can eat buffet. They should still pose a real threat.
*I don't want AI to be unable to deal with them... the barbarians should not be able to wipe out players or disproportionately hinder one AI play style (peaceful, warmonger, etc) much more than another even at raging levels
Also:
I think there is too much of a jump in power from upgrading units at the moment. Wars are long and slow until one civ researches a military tech and upgrades units and wins effortlessly. Such a big focus on upgrading in turn puts a big focus on science which is already of paramount importance in the game. I think if the AI can handle it, much more importance should be placed on flanking. It shouldn't require a lot of upgrades for flanking to be a big advantage. Even if all units/soldiers involved were completely untrained a flank would make a huge difference and would probably be the determining factor in a fight. Boosted flanking would add more tactics into combat and need for skirmishers. But MOST important, an army that's just one upgrade above won't be so invincible.
Easiest way I can think to do this:
Decrease spawn rate to previous levels, but Raging Barbarians upgrades barb units to the next tech level up than they would normally be. Warrior->Spearman, Archer->Comp. etc. This way barbs could be less frequent and more potent.
Barbs don't wander more than 4 tiles from their spawning encampment until the second era.
Barbs can't enter Civ borders or attack cities until second era.
Barbs can't build ships before civs (come on, civs have a libraries and scientists and stuff, how are barbs able to beat us to ship building?)
All land and sea units flanking bonus greatly increased right off the bat without any upgrades (then the upgrades should be toned down proportionally)