Please note that this is written from the perspective of a 70 Restoration Druid, so unfortunately I can't comment on whether Priests, Shamans, or Paladins might have had an easier or harder time healing the instances. I have a good but not jaw-dropping resto set, and on the live realms clock in around +1998 to +2100 healing unbuffed. If your gear's better or worse, then just adjust the potential difficulty level as needed. And even if you're not a healer, you still might find something useful here:
So far I've healed Utgarde Keep twice, Azjol-Nerub three times, and Anh'Kahet once. AK is technically beyond my level range at 74-76 (my main is still 70 in the beta) but is doable as a healer if your party's gear is decent, people aren't stupid, and your tank is 74+. The TLDR version of this article: the 5-man dungeon experience in Wrath has been enormously (and positively) affected by players' access to quality gear outside of raids, and you will probably have fewer issues with early dungeoneering than you did in BC. I haven't seen any dungeons apart from these yet, but the three I saw were wonderfully designed, fun to heal, and -- words fail me, just plain beautiful. The level of detail is stunning.
- Have healed two Paladin tanks so far, one in Tier 4 and badge gear, and the other in a mixture of Tier 4, Tier 5, and Northrend quest rewards. Paladins continue to be excellent AoE tanks, which is extremely helpful in Azjol-Nerub especially. Don't believe Blizzard when they say they're downsizing the number of mobs per pull, but even large add waves are far more manageable than what you might be used to from Shattered Halls (it might be more accurate to say that most trash pulls are smaller, but there are still plenty of AoE tanking situations in all three dungeons). Both paladins were generally easy to heal; if you have a Kara or better geared tank in the early Wrath dungeons, they're unlikely to suffer big damage spikes.
- For Utgarde Keep I had a Warrior in Tier 6 with some DPS pieces sprinkled in. Easiest to heal of all four tanks if for no other reason than gear, I suppose, and our group (warrior, me, retribution paladin, shadow priest, and demonology warlock) literally chain-pulled the whole dungeon, bosses included. Warrior AoE tanking has improved tremendously since Burning Crusade, so you don't have to worry as much about getting your face smashed after an early heal. Excellent single-target threat as well. You may wind up healing the group more than you heal them.
- Unfortunately I have not yet healed a Druid tank in the beta so I'm not sure how they're faring. I can tell you that in the beta I am down roughly 11,000 armor in bear form while feral, to what effect in early dungeons I don't yet know. Druid threat (both single target and AoE) seems to have been given a large boost, however, and Blizzard is still fiddling with the new Protector of the Pack talent. I'll respec feral this week and see what I can find out for you.
- Death Knight tanks: I've only had one of these so I don't know if this guy was representative, although his gear likely was (I'm assuming that most DK players will continue to level through Outland to hit Northrend as early as possible). It could have been a player skill issue and there will likely be an element of that to all DK's (not having had the benefit of playing the class from level 1 onwards), or...well, it could just be the class or spec. It's probably too early to tell. He was by far the hardest to heal with the largest and most frequent damage spikes, and the only tank for whom I had to stop and drink on a regular basis, or blow Innervate for on a boss fight. At the raid level Death Knights are clearly intended to specialize more as spellcaster tanks; versus heavy melee damage, I don't know that they'll do as well. Until they've achieved gear parity with their pre-BC tanking brethren, I'm withholding judgment, but if you're healing one, be prepared to have an Oh Shit ability or two hotkeyed. If the guy I had tanking Azjol-Nerub is indeed representative, then expect your average DK to be a serviceable 5-man tank who can hold aggro well, but they may require more healing attention than other tanks. This got hairy on boss fights, but again, I've only had one DK tank so far.
- Tanks seem to have far fewer issues holding aggro so far, and the trend seems to be away from the crowd-control mania you saw in BC. This does, however, mean more mobs on the tank, so plan accordingly.
- On average trash pulls, there's not a ton of AoE or group damage, but keep an eye on your melee in Utgarde Keep especially. I still don't know how this happened, but our ret pally got wrecked in the dragon room and I'm not sure whether he got cleaved or if he momentarily pulled aggro or what. With that said, he was also a poorly-geared alt who'd arrived in Northrend in greens and was rocking about 6.5K health, so whatever the hell hit him would probably have less effect on a player who'd spent more time at 70 in Outland (most of my groups' DPS had badge gear, Season 2, and/or various tier/Kara/ZA pieces). On the last two-mob pull before Anub'arak in Azjol-Nerub, the mobs have a drain ability similar to Hex Lord's (wait for it to wear off before you start pestering ye olde lore figure) and a type of shadow damage debuff that can produce some fairly insane burst. However, this happened the first time and not the latter two times I did Azjol-Nerub, so I'm not sure what triggers it or how. Keep people topped off just in case.
- BOSSES: there's nothing out of the ordinary from a healer's perspective on bosses in Utgarde Keep (not to say they're uninteresting, just that there's nothing you really need to worry about that I can remember). In Azjol-Nerub, watch out for poisons in the trash waves before the first boss (Krik'thir). A random member of the group will also be encased in spiderwebs every wave and be unable to move or cast until the group destroys the web sac. It doesn't seem to have much health (two Moonfires will take care of it if you're a Druid) so you can often take care of this yourself. Tank threat is usually sufficient on these waves that you don't need to worry about being eaten alive, but keep an eye on your clothies both here and on Krik'thir. Krik'thir has an AoE curse and summons a metric ton of non-elite adds. They don't hit for very much, but there are a lot of them (see picture earlier in the article); again, watch the squishy people. The next boss, Hadronox, has an AoE poison, but more importantly, will heal himself for a ton of health if he kills a player or an NPC mob. You can't do anything about the mobs he'll kill while your group deals with trash waves, but try not to lose any group members once the tank engages him. Anub'arak, pictured above, is (again) an add fight. He'll dig underground at intervals and summon waves of adds, some elites but mostly non-elites. Again, they don't hit too hard individually, but there are an awful lot of them. Watch your clothies (and yourself!) and keep your tank topped for when Anub'arak re-emerges. He doesn't wipe aggro in between.
- ANH'KAHET: this is a level 74-76 dungeon that's pretty much at the upper limits of what you can expect to heal at 70.Trash is unremarkable until the larger packs you'll pull before the third boss; these will hit your tank fairly hard, but be very careful about pre-healing because you want them on you even less. That was actually the only wipe on trash I ever had; a higher-level healer may have less difficulty with it. Boss encounters -- Prince Taldaram, Elder Nakox, Jedoga Shadowseeker, and Herald Volazj -- are all quite interesting but (with the exception of Prince) add fights to varying degrees. Elder summons non-elite adds that will have to be AoE'd down, unless you have enough DPS just to focus on the boss and heal through the damage (as the tank advised my group). Use your best judgment here; on a well-geared tank, Elder doesn't seem to hit too hard, so you should have enough GCD's to spare for the group. Jedoga, similarly, is an encounter that will depend entirely on your DPS. She gains power for each acolyte making it to the center of her platform to be sacrificed, so DPS needs to unload on these guys ASAP. If your group is slow at moving out of her AoE ability, you'll also have a lot of damage to mop up. If the acolytes get mowed down in enough time and people avoid the AoE, you're unlikely to have problems. Old Gods will start whispering you in this portion of the dungeon like C'thun, which is a really fun little touch and a lot more entertaining than general channel chat gems like "HOW I GET HORS?" When you roll a Death Knight that joke will suddenly make brilliant sense, I promise.
Herald Volazj is an entertaining fight -- the best and most memorable of the early dungeons -- although as a 70 it was more difficult than I expect it would be for a level-appropriate healer. If you've done the last boss in Auchenai Crypts or Leotheras the Blind, you've seen a similar mechanic, although this one's a lot more fun. Volazj will force each player into a shadow realm with a debuff called Insanity where you have to kill copies of your group's characters in order to get out. And yes, they ALL attack you at once. As you might expect, with tank damage going up in Wrath, healers will probably have a harder time with this than anyone else, so you may want to pack a few pieces of more damage-oriented gear. Then again, with all +damage and +healing being condensed into the single +spellpower stat, that's probably not necessary and is possibly more a reflection of my healing a 74-76 dungeon at 70. I had trouble initially but used Barkskin and Hurricane to kill the melee toons, and then used Moonfire and Wrath on the ranged. It's more mana-intensive for healers to kill their adds, you'll need to mop up add damage on your group (you'll usually get a glimpse of "yourself" trying to kill your group members) and Volazj will do respectable melee damage on your tank, so pack some mana pots just in case. All in all a very fun dungeon and you'll probably enjoy the last fight a lot.
And God bless whatever developer gave Druids an out-of-combat resurrection. I didn't get to use it much, but I squealed like a little girl whenever someone died. Huh. That might be why my guild doesn't let me heal anymore.