Since the other thread is mainly regarding the visual appearance of Tier 21, rather than the effects.
Keep in mind, this is a very early look, as T21 is still quite a ways off. Likewise, all of this is subject to change, though it gives us some idea of what to look forward to.
The Arms 2p reads as though it's a debuff applied alongside Colossus Smash, meaning it should apply to multiple target, and be incredibly potent alongside Bladestorm/Ravager during Battle Cry. It also,
- Boosts the weight of crit slightly.
- Increases the value of Precise Strikes and Deathblow (artifact traits).
- Very likely double-dips with Corrupted Blood (increase crit damage of ability, damage rolls into CBlood, increases crit damage of CBlood).
- Synergizes very well with Titanic Might (maybe too well, considering Rend/TM are already dominant talents) and Weight of the Earth (legendary pants).
The Arms 4p seems simple, but being able to stack gives it a surprising amount of depth.
- Above 20%, it's passive, and the stacking mechanic allows it to function even during chain Tactician procs.
- Below 20%, the buff can be stacked while rotating Mortal Strike and Execute, until a greatly empowered Whirlwind/Slam is built up with a high +damage and +crit chance, which should then benefit from the 2p +crit damage.
The Fury 2p causes Rampage to bleed, similar to Bloodbath. It reads as though only the primary target (similar to the legendary pants) gets the bleed, and doesn't count damage cleaved onto other targets via Meat Cleaver. That said it works with every Rampage, and...
- Synergizes well with Reckless Abandon, Massacre, the Soul of the Battlelord (legendary ring), and the Valarjar Berserkers (legendary pants), especially during Battle Cry.
- Benefits from Frothing Berserker, since the bleed is based on Rampage's own damage.
- Has potential for double-dipping; if the damage increase from Frothing Berserker, Unrivaled Strength, Enrage, etc, apply to both Rampage, making the bleed bigger, and the bleed itself after the fact.
The Fury 4p reads as though it does increase all Rampage damage, including cleaved damage. However, it also only specifies Rampage, which means it could be contentious below 20%.
- Without Massacre, the bonus would have to be very large to be worth spending 3.4 Executes worth of rage and losing Juggernaut stacks.
- Being based off Battle Cry, it heavily favors Convergence of Fates, although it's been implied that the trinket will be nerfed by T21.
- Actually doesn't favor Reckless Abandon or the Valarjar Berserkers, since it only buffs one Rampage per Battle Cry.
Overall, I like the bonuses, though they may favor certain talents and legendaries a bit too much (although at this point, I'm not sure it's possible not to). My major concern is with the Fury bonuses use of Rampage during Execute. In the Reddit AMA, the designers spoke about rebalancing Massacre, so this may be an intentional choice to reinforce the use of that talent/legendary ring, or it could simply be oversight. Of course, we have to wait for numbers before we can determine how strong the bonuses and any opportunity cost will be, though personally, I'm hoping that the Fury 4p isn't an oversight, and is a prelude to reworking Fury Execute... but I'm not holding my breath just yet!