And to a lesser extent Exalted Soul and Vengeance.
These seem like absolutely necessary passive skills. I'm interested to see counters to this claim of builds you think will be viable without using these passives. For the barbarian example you might not need both Animosity AND Unforgiving, but you also might want both to maximize Dread Shot. Either way, not having eaither seems like gimping your character somewhat. Thoughts?
It's based on your gear and build... they aren't necessary. Gear is the most important thing in D3. If you have a lot of skills using a high amount of mana with no mana runes and you haven't stacked mana regen, you'll need one of those skills. Or if you want to stack mana regen and be able to spam something like locust swarm you would possibly need one of those mana regen skills on top of it if you have no mana regen runes.
Normally I need 4 Cleaves to be able to throw one Hammer of the Ancients. Animosity reduces this to 3,63 Cleaves per Hammer. The average damage per attack of these rotations is 4*120+1*200 / 5 = 136 for no Animosity and 3,63*120+1*200 / 4,63 = 137,27 for rotation with Animosity. Hardly a difference from dps point of view since generators are actually decent source of dps themselves.
The power of Animosity is in other skills that benefit from fury gained, for example lenghtening Wrath of the Berserker duration via Thrive on Chaos rune, and being able to unload longer burst of spenders in one go against hard bosses and other tricky situations.
It also gets better the more sources of fury other than the three primary skills you have. These include runes for the primary skills and things like Leap and Ground Stomp which also generate fury.
For a build optimised for Animosity I'd guess about 5% dps increase and added benefit of more fury for non-dps purposes.
You don't really need to wait for the game to come out to know which stats you need.
Stack mana regen = use Vision Quest. Stack Max mana without health globe heals = Spiritual Attunement. Mana with health globe heals = Gruesome Feast. Of course you can combine them and do a lot of different stuff. But unlike some of the other categories, at this point I'm pretty sure Mana is only affected by the per sec regen and max mana modifiers. Most people will probably use skills for the bulk of their regen. But if you need more you'll go with either one of those and stack it with an appropriate passive if need be.
Those skills could be anything from useless to must-haves. It all depends on what sorts of modifiers gear will have and whether Blizzard decides to add resource scaling for skills. As it is in the beta, I'm guessing equipment with +max resource and +resource regen modifiers are going to scale, but only Witch Doctor's skills have scaling costs.