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Continuing from my post on how to spec your disc priest in 4.0/Cataclysm, let's take a look at what talents could be interesting for the holy priest. My first impression overall is that disc has changed more than holy, but I am more positive about the fun healing as holy might be in Cataclysm than I initially were. At one point I even considered not speccing holy at all for Cataclysm, because it just seemed like the same old thing, except maybe for Chakra. Alot has happened since then however, and I am sure alot more will happen before we have holy healing set in stone for Cataclysm. Don't forget to bear that in mind for this post by the way, things really do change from one day to the next now and this is therefore more of a general map of thoughts than the definite answer on how to spec your holy priest.
TL;DR - Suggestion on a build at the bottom.
As with the disc talents I won't discuss the obvious choices in the main tree, that's for another post. Instead I'd like to highlight the questionmarks, the talents that might need some testing before we can say which way it should be. Something I didn't mention in my other post however and that could be good to keep in mind is that these talents aren't optimized for Wrath, after all they're Cataclysm talents. That means healing might seem off at first, we won't know for sure how we're supposed to do things until the real things hits us.
The big difference between discipline and holy (except the same old one, disc being about shields and holy being about aoe-heals) seems to be that holy is way less about smiting than disc. As a disc you'll probably want to use smite as part of your standard healing arsenal, see my post on disc talents for more info about that. But as a holy you won't be able to spec Atonement, the talent that turns Smite into a heal, which makes me think we won't want to smite as often as holy. If at all. Also unlike discipline, holy wouldn't want to spend as many points in the off trees, leaving plenty of points for the main tree. Nearly all of them in fact, so even though I'm not entirely sure of the usefulness of all the talents, we'll have to spend points in them anyway since there's really nothing else to take. So let's take a look shall we.
The main tree (holy) - talents not mentioned here are the ones you probably should talent.
Divine Fury - Although holy healing still is alot about using instants, Heal will be one our most important healing spells in Cataclysm. Therefore this will be one of the most important talents to keep up with the haste drop (and at all times), and besides, there's not much else better to take anyway!
Desperate Prayer - Desperate Prayer is a very small heal, and not a great talent. But because Surge of Light is an even worse talent we still have to pick this to get further down the tree. It could be a nice saver when you need it, since it is free of mana and instant.
Surge of Light - This used to be one of the best talents in the holy tree, until they revamped to proc 6% from all Heals and Smites instead of half of your crits. It might've been too good before, although I don't think so, but it definitely sucks now. Even when raiding, where you'll throw shitloads of Heals, this just won't proc often enough to make any difference whatsoever. The mana efficiency is marginal at best, and I really feel they need to buff this alot before it's worth those 2 tp.
Lightwell - This poor spell seems to finally get the attention and overhaul it needs. With an increased range, no requirement of targetting and even bigger healing output, I'm seriously starting to think this might become a really good talent. I've always talented this spell (and generally get the response "Oh look, a lightwell!" from surprised people on TS) but that has been more out of sentimental reasons than the skill actually being good. Now it seems Lightwell might be as awesome as it always deserved to be.
Serendipity - You won't use this often, but when you do you'll be glad you have it. Haste will go down significantly from 80 to 85, and this will be our "oh shit" talent. When the tank is dangerously low on hp you throw two flash heals followed by a Greater Heal so save the situation.
Spirit of Redemption - The main reason people ever specced into this was for the extra 5% spirit and/or to get down to Lightwell. SoR doesn't provide any of those anymore, and eventhough it can occasionally be useful, I don't like to talent in a way that expects me to die.
Tome of Light - Only useful if we also spec Chakra and Revelations, but since Chakra is what being holy is all about in Cataclysm that won't be a problem. I am somewhat uncertain as to how useful this talent actually will be, but we have to talent basically everything to get all the way down into the tree anyway.
Blessed Resilience - The changes to this talent (and the corresponding in the discipline tree, Focused Will) have made them less of pvp-talents, and actually possibly very useful for pve. But maybe still not useful enough to warrant it taking talent points from something else.
The offspec trees
Mental Agility - I do believe Renew will still be a big part of our healing, although maybe less so than it is right now. Still this talent also improves CoH and PoM, two other very important spells in the holy arsenal. I also think mana might be more of an issue for holy than for disc (just as now) seeing as disc has more talents to improve mana efficiency than holy does.
Twin Disciplines - Since it increases both healing and damage done by 6% it is clear disc priests are the ones who will benefit the most from this talent. That doesn't mean it's worthless for everyone else. Like mentioned I don't think holy priests will be smiting very much, so they'll probably "just" be using the extra healing. 6% extra healing straight off is fairly good, and if you don't feel like you're having any issues with mana you could easily take this talent instead of Veiled Shadows or Mental Agility. It all depends on how much mana will be an issue in Cataclysm. Since I am gemmed for disc I have tons of spellpower but low mana regen and could use Mental Agility more than Twin Disciplines. Even in Wrath holies have been among the healers (together with resto shamans) who yell for innervates, but only you know if you're that priest or not! ^^
Evangelism (and Archangel) - Although it is possible to spec into Evangelism and Archangel even as holy, I don't think it would be something we want to do. Without Atonement we won't have the time to Smite anyway.
Darkness - Holy has no talent to improve haste. Haste is as important as it was in Wrath so this is a great talent.
Veiled Shadows - A decent way to improve mana efficiency for holy, but Mental Agility is at least twice as good.
So my first try out for a 4.0 holy spec would look something like this.
UPDATE 13/12: Here is the spec I'd go with for level 85.
That means we will try to keep renews up by using Heals, all the while trying to manage to keep the proper Chakra active and using our different corresponding Holy Words as fillers. Managing our Chakra states will be what will separate the wheat from the chaff when it comes to holy healing, so practice, practice, practice on evaluating the situation and choosing the right chakra stance, it will make a big difference. As it is now I personally feel that Chakra: Heal (Serenity) is almost always more efficient than Chakra: PoM (Sanctuary).