I guess given that it's my main spec and it's going through some big changes, we should probably talk about Protection Paladins. There's plenty of nit and grit to get into here, but I'm going to try to keep it relatively simple.
Holy Power Gone:
Yes, Holy Power is now a Retribution-only feature. So how do we actually work then? The main thing is that Shield of the Righteous, which remains our central active mitigation ability, now has three charges.
You can kind of think of ShotR charges as your new resource to track, though unfortunately it's not a part of the default UI. I imagine you'll be able to put together a Weak Aura to track them, but you aren't going to have anything quite as elegant as the little holy symbols under your mana bar.
Judgment's main purpose in your rotation now, other than generating threat, is that it will reduce the remaining recharge on your Shield of the Righteous by one second, or two on a crit (not sure if this will be enough to make us gear for crit.)
This was maybe a long time coming. Stuff like Seals and Stances and really anything that you toggle on and off that isn't a single-target/aoe option tends to be something you set once and then just ignore. So I'm not really broken up about this.
Less Healing Independence:
Light of the Protector replaces Word of Glory for Prot. This ability is on a relatively short cooldown and heals you for a percentage of your missing health. Thus it becomes more useful the closer you are to dying, which is, granted, when you'd want to be using Word of Glory too.
The downside of course is that you'll never be able to heal yourself up to full with this ability. I've had Word of Glory with full Bastion of Glory stacks work about as well as a Lay on Hands in nasty situations - I remember when my guild got our first kill of the guard dogs at the start of Mogu'shan Vaults, I was the only raid member alive for the last maybe five percent of the fight, thanks to my great self-healing abilities.
Consecration, which has an improved graphic (actually, almost all melee classes have lots of improved graphics,) is now pretty central to how you function as a tank. Standing inside it will buff the effect of Shield of the Righteous and Light of the Protector, and it'll also give Hammer of the Righteous its AoE component. There is, however, a talent that you can take to opt out of this, as you'll get the Consecration bonuses at all times (it also makes Hammer of the Righteous have no cooldown.)
The downside is that there's no glyph of the Consecrator anymore. So you'll need to pick your spot well when you throw this down. You can, with enough haste, reduce the cooldown on this below its duration, allowing you to have multiple Consecrations down at a time.
Hammer of the Righteous:
Crusader Strike has effectively been merged into Hammer of the Righteous for Protection. As seen above, Hammer of the Righteous is single-target by default, but gets its AoE effect from standing inside your own Consecration, or through a talent that causes it to always do this and also have no cooldown.
With the removal of Holy Power, however, you'll really only use this ability as a filler. You'll prioritize Consecration, Judgment, and Avenger's Shield first, and of course weave in Shield of the Righteous any time the buff's falling off or you have a big attack to block. It can be used for snap-threat, but if you're going into an instance where this could be something you need to do, I'd recommend taking the talent that gives it its AoE component outside of Consecration.
Lightin' the Way:
I've got to confess that of all the spec re-works in Legion, this one makes me the most concerned, which makes me a little nervous due to the fact that this is my main spec of my main character. It does seem functional (I have yet to run things in a proper dungeon or raid group, but at least during demon invasions I haven't felt too squishy,) but I think that some of the design choices are a step backward. My mistrust of active mitigation before Mists of Pandaria is well-documented on this very blog, but once I got my hands on it I became a true believer.
But I also think that the design of having tanks build up resources and then spend them on defensive abilities was a really integral part of that initial active mitigation design. Ironically, the two classes I most consistently play as tanks are having this turned around - simply getting ability charges and then a way to speed up that recharge. There's much less of a sense of "hit it now" with the new design, and more of a "hit it whenever" feeling.
Don't expect me to drop Prot as my main spec or anything, and it might be that with proper addon management like Weak Auras, I'll have enough information on-screen for me to feel like I've got a strong handle on the spec, but we'll just say that for now, I moderately disagree with the direction that Blizzard has gone with the spec.