What new and different abilities do you have at 100? What should Blizzard have changed but didn't? What should we know about while we're raiding with you?
I'll start with:
Disc
Discipline Priests have even more bubbles and rely even more on shielding. Despite this, there's plenty of damage to go around and with the loss of smart healing, we're not bubbling off all your damage now. Atonement is primarily a way to build stacks to buff our healing.
We lost Renew so no more HoTs on the move. We also lost Binding Heal, I think Disc priests in general are missing that the most. A couple more abilities aren't instant casts anymore but we're still fairly mobile with Power Word: Shield. Prayer of Mending doesn't bounce as much with our beefy bubbles out there but we can have more than one on the raid. Prayer of Healing is still per group so we're still going to be asking for groups of 5 instead of allowing creative grouping so we can contribute to AoE healing. Holy Nova, set to be our AoE heal, was nerfed into near oblivion after some abuse at lvl 90.
We've got a strong single target bubble in our lvl 100 talent Clarity of Will. This is our big tank protection bubble, it stacks multiple casts up to 50% of the target's HP and lasts 20 seconds, giving us plenty of time to refresh unused stacks. One downside is that tanks don't appear to be taking damage until the bubble wears off and then appear to be taking lots of it, making the incoming damage harder to judge for other healers.
We like Crit and Mastery > Haste > Multistrike (doesn't proc little DA bubbles) & Versatility (sucks).
Shadow
Shadow has reasonable single target but weak AoE damage. We can still multi-dot two or three targets fairly effectively but Mind Sear is only worth casting at all when it will hit 10+ targets.
Our level 100 talents each significantly change our rotation. Clarity of Power turns us into stationary 3 button heroes or with a little more work and alternating between a simple and a complex rotation, our strongest single target damage. CoP is also probably the most flexible spec for dungeons, PVP, and raiding. Void Entropy adds an extra DoT and Auspicious Spirits turns our Apparitions into extra orbs, both specs possibly good for movement and multi-target fights.
Shadow Priest stat priority is mixed depending on talents but Crit, Haste, and Multistrike are good for CoP.
I pretty much sat out of the last two expansions, so I can't tell you what's new to protadins unless you want everything from WotLK...now. Um... BoK is no longer five minutes? :D
Haha, so true, so much has changed over the expansions. I log into alts I used to play regularly and feel lost apart from the simple and obvious mechanics and even some of those are behind talents or glyphs.
Prot Paladins lost our devotion aura raid cooldown as well as our dps cooldown, avenging wrath. We still have good self-heals, but not nearly as stupid as they were last tier. Instead of putting a huge HoT on ourselves, we'll usually be using Sacred Shield which is a kind of rolling bubble. As usual, our mobility and our ability to pick up groups of adds is limited. Holy Wrath got increased to give us a slightly better snap aggro on packs of adds, but still nothing like some other tanks have.
For gear, we are "attuned" to Haste but sims show it is actually our worst stat. Blizzard has been implementing hotfixes to improve Haste for us but so far has not succeeded. It is possible that they will try again. For now, we prefer Mastery by a wide margin (after Bonus Armor and Stamina), but that could still change.