Here are random thoughts on playing a Holy priest in various and sundry Cataclysm raids.
Chakra: Sanctuary is the norm for me while raiding. Area heals are something we do particularly well, and-- unlike in 5-mans where the tank takes most of the damage and you can milk Serenity for its mad efficiency-- there's lots of area damage to go around. There are particular fights and situations where Serenity is good, and appropriate, but Sanctuary is my default.
I see some priests running around with Inner Will. I generally disapprove of this. Inner Will only cuts the mana costs of some of your spells, whereas Inner Fire boosts the throughput of your whole arsenal. Proper cooldown use and knowledge of the fights will allow you to manage your mana effectively, and facilitate using Inner Fire over Inner Will. Therefore, we'll treat Inner Fire as the default setting, and I'll discuss specific instances where Will might be advisable.
Most sources of AoE damage in Cataclysm are *very* predictable. If you go into the battle with a plan on when you're going to use Sanctuary and Divine Hymn, you'll reap the rewards.
"Speed Bubble" = Shield with the Body and Soul talent.
Uses of Lifegrip: 94% annoying guildies during down-time/run-back, 5% pulling people away from certain death, 1% killing AFKers. Certain people die a lot to the elevator boss in Blackwing Descent. You know who they are. When you see them trying to be clever, a well-timed Lifegrip can give you a legendary reputation.
This fight reminds you that you have a spell called "Mass Dispel". Yay. Chakra: Sanctuary is a beast here... as predictable as the AoE is, Sanctuary can do significant healing, particularly on 25-man, while Circle and Prayer mop up. Renew and Circle make the Firestorm portion a breeze.
Save Sanctuary for his raid-wide damage spell, Lava Spew; you waste it if you blow it on the random multi-player hits. Circle is better. Prayer of Mending is also good if you cast it on a tank shortly before the Spew, or on the parasite tank and his buddy. I like to use my Shadowfiend the first time his head's exposed and my Hymn of Hope the second, for the token extra damage; if you're having mana problems, a very early Fiend (say, 45-60 seconds in) could allow a second cast, depending on your spec.
On normal, a Speed Bubble can really help out the Flamethrower target. The regen from Arcanotron is quite nice. Remind people about your Lightwell. Know which bad guys to use your Hymn of Hope on. Toxotron/Arcanotron is a good combo. Wait for the poison cloud and adds to expire, then go (ideally inside the regen puddle to boot). You can plan to use Divine Hymn on one of the Magmatron AoEs, or you can save it in case someone is stupid and attacks a shield.
Yeah, he's kinda easy. I like to Hymn of Hope during a blue phase, holy nova during green phase, top healing during red phase, and Divine Hymn after the AoE during the burn phase. Pretty blah.
Conceivably, Inner Will would be a good swap during the air phase, since you're constantly on the move and using primarily Renew and Circle. Swap back to Inner Fire when Atramedes lands. The two most important things to do, though, are a) not get hit by stuff, and b) Speed Bubble your fire kiter. You know, the rogue that's running around like a madman after he hits the gong and the fire's chasing him. Position yourself within 40 yards of his kite path (harder than it sounds), watch him as he Sprints around, and hit him with a Speed Bubble immediately as Spring expires. He will love you for this.
You may think it's a good idea to use Lifegrip in a similar fashion. It's not, even if you're on his kite path. You're an eligible target for Sonar Pulse; therefore, you stand a substantial risk of yanking your kiter directly into a Sonar Pulse, or littering his kite path with Pulses/fire. This will have gruesome results. Just don't.
On 10-man, use Heal/Serenity on people when they get hit; on 25, use CoH and Renew. Why the difference? The healer/raider ratio is lower on 25-man than on 10; with more people getting hit, there's more ground to cover, and Renew/CoH is faster. (I'm assuming you have all the applicable Renew talents here.) If a bile shot comes up immediately before a Massacre, you may have to get inefficient to cover the difference. That's okay. This is not a regen-intensive fight. You just have to last until the bad guy gets low; right before you push him over, blow all the mana you've got left to get people topped off before the burn phase. Your pitiful DPS is probably not going to be the difference, so don't sweat going OOM as you push him over. However, if you *do* have mana to spare, don't forget to go Chakra: Chastise for the extra damage!
This fight is amazing! Way cooler than Cho'gal in my opinion. I start the fight in Sanctuary to quickly heal up fall damage, then swap to Serenity to keep the kiters and tanks up. Once the Electrocutes start coming it's back to Sanctuary, using Sanc, CoH, and Prayer to recover while rolling Renews on the tanks (this involves a fair amount of running).
You can use Lifegrip on people who have trouble with lava, but that's a quick fix only. If people have problems repeatedly, verbal abuse or computer upgrades seem to be the only solutions.
I tried a bunch of different ways to do the pillar healing, this seemed to work best:
1) Get a PoM on yourself as the lava rises.
2) Use CoH while swimming.
3) Drop Sanctuary on top of the pillar.
4) Flash/Renew people at critical health.
5) Drop a Lightwell, and probably another round of PoM and Circle.
6) Swap to Serenity and use Serenity, Heal, PoM and Circle to last the rest.
The initial phase of the pillar healing is incredibly mana-intensive; I tend to drop down to around 20k mana before I stabilize. That's okay! There's regen opportunities after the pillar phase is over. On 10-man you can keep Renew rolling on everyone on your pillar, using Heal and Serenity to keep it up while PoM bounces. On 25, the number of people you're healing makes this prohibitively expensive. Any inefficiency results in you going OOM. If someone gets unusually low, Renew and keep it up with Heal after mixing in a couple Heals on others, but you really have to trust your healing partner on your pillar and NOT PANIC to make it through.
Once Nefarian lands I pop my Fiend, then Hymn of Hope after the first post-landing Electrocute (if I have above-average mana I'll wait and use both after the Electrocute). After that the fight gets pretty easy for a healer.
I'll post again with Bastion thoughts later.