I am a great fan of Barbarian cards and I use them pretty frequently, but I have observed that the secondary keyword bonus that has been implememnted recently (If there is no wall to destroy, enemy stock will be lowered by the same amount instead C-3, U-8, R-15) is way too strong. It's a nice idea, but I think we should restraint the stock-lowering. It's stronger than Brigand (Brigand - basic gain 10, bonus gain 10, side-effect (Robbery): additional stock will be stolen from opponent, amount based on played card rarity (Common - 1 stock, Uncommon - 2 stock, Rare - 3 stock).) which supposingly is the "thieving" keyword.
The reason it's so strong is not only that it lowers the stock by that much but it also does it when the opponent has no wall. By also lowering the stock, you are basically creepling the opponent as they can not mount a defense for 2-3 rounds, until they can gather resources to build up their wall or to attack. A common Barbarian will trigger the same effect as a rare Brigand would. Not only that, but the Barbarian keyword is filled much more easier than the Brigand keyword.
Perhaps lower the amount by which stock is reduced to C-3, U-4, R-5. (I am opposed at lowering it to the levels of Brigand, as that would make the side-effect too weak, since Brigand can lower the stock even more, as every card played is one that lowers enemy stock)