I've really only run two of the instances (haven't gotten past level 71 yet on either shaman, and since they just doubled experience costs it may be a while before I do) so I'm only conversant with the Nexus and Utgarde Keep. Without spoiling the bosses for you, I'll just say that Utgarde Keep is the easier one to heal (it may even be fair to say it's just plain easier) but both are doable for even a moderately geared restoration shaman. To some degree, those of us with decent resto and elemental sets will benefit from gear consolidation due to the spell power changes: my Mazthoril Honor Shield is now my healing shield and the spell crit helps proc my Ancestral Awakening ability.
Some of the new abilities are very powerful tools for healing, if you can grasp when to use them effectively. (I say this as someone who failed to do this my first Nexus run.) Spirit Link breaks on certain conditions, it's true, but if it manages to signicantly lower the health of someone who then takes more damage from another source, you need to be fast on the healing to compensate. It did, however, save the tank twice, and the Death Knight was pretty good about me constantly lowering his health like that without warning him.
I have to say that even with full Healing Grace I felt like I was putting out quite a lot of threat when the healing need got higher. Several times on the Nexus run and on one of the Utgarde runs I constantly seemed to be riding on the tank's threat just using Chain Heal and Healing Wave: a use of Tidal Force on the first boss in Utgarde when the tank and our two melee DPS were all very low on health resulted in the boss and several skeletons all coming to say hello to me. Luckily, shaman fade was on cooldown. I'm not sure if it's just due to my having used max rank there (incoming complaint about the downranking nerf) and the crit just being a lot of healing all at once or if it's just a case of our threat just being higher than before or what.
Most people ask about the spell power system, so I'll cover it somewhat here. Using the old system, I had about 1300 plus healing on my restoration set alliance side and maybe 1600 or so horde side. I seem to be roughly at 700 or so alliance and nearly 900 horde side now. It depends on what elemental pieces I use in each kit and what totems I drop. My heals haven't gone down, though. If anything, my max rank heals hit harder, especially with talents like Blessing of the Eternals and a significant amount of spell crit on my gear that I didn't have before. With both Flametongue Totem and Wrath of Air down, not only are the heals hitting harder but I'm getting more off in less time, although of course 5% isn't terribly noticeable. As of yet I've not even seen another shaman in any runs I've done, unfortunately, so no testing of totem stacking. The spell power system may or may not be confusing for people used to the current one, but so far I can't report that it in any way affects the strength of your healin in a negative fashion.
Rank three Ancestral Awakening isn't quite a gimmick spell. It had several nice procs while healing in the Nexus. But it's hard to say that it's really essential or worthwhile at this point: it often procs to no real effect, healing a tank who is almost to full because he's the only one in the party tanking any damage. When lots of damage is flying around and it would be nice, you're often using chain heal anyway, and it doesn't proc off of chain heal. I'm thinking it's an attempt to try and get shamans to cast healing wave more often: in a situation where there's some, but not a ton, of splash damage than it can be pretty nice. I would like to see it buffed. Everything else about deep restoration seems really excellent to me Tidal Waves made me actually throw healing wave around a lot more as it reduces the cast time significantly (35% with WoA going) and with having healing wave already talented down to 2.5 seconds, my calculator tells me that's a 1.6 second healing wave. If I'm wrong, blame calcy. He hates me. He's always hated me. Bastard.
It's possible the threat I was noticing was simply the result of me casting a lot more heals in the same time on harder fights. I'm not sure what I'd be able to do to combat that, though, and its possible (as loath as I am to suggest so) that our warrior tank simply didn't generate very much threat. The warrior who tanked the Nexus and the paladin who tanked my second Utgarde run didn't seem to have as many issues with aggro, but there were a few bad patches, which might also be attributable to learning the instances. I'll keep my eye on my threat as I continue and as I play elemental more in the upcoming week and get back to you.
In the end, I didn't seem to have any significant problems at all. Healing hasn't changed terribly much, it's just got some interesting tools added. I specced for Nature's Guardian on my first run (the one with the most aggro problems) and specced out for the second and third, and honestly it didn't seem to proc. I remember someone asked me to take it, so I wish I had better news for you on that front, but even at 50% chance it didn't go off more than once that I can recall, and even with it I still had aggro. The heal was nice, though.
Earthliving weapon still doesn't have any ranks above rank one. I used it anyway, didn't see the HoT go off. It's impossible to evaluate it until it gets more ranks, sadly.
Okay, now that we've discussed how resto is shaping up (more or less, really nicely, with some possible threat issues) I'll address the downranking issue. It's going to really change how I heal, that's for sure. I often spam lower-rank chain heals in tight situations to save mana and keep everyone taking AoE damage topped off. I won't be doing that anymore. I won't be using lower ranks of healing wave to make sure the tank has healing way on him before running in on a boss, either. I use downranking to help my mana efficency (which is admittedly a lot better now thanks to Water Shield) and I know a lot of shamans use it for a low cost interrupt in PvP. (I can't complain about that, as I don't PvP resto.) I'm not sure how I'm going to compensate for this change. I'll do so, of course, but I don't know how yet and I don't like the idea of being forced to heal less and let the people I'm healing take more damage until I figure out how to cope. I'm hoping that Blizzard is taking a really long, hard look at boss design especially in the raids, but even in five mans there are times where I'm seeing a lot of damage happening really fast to more than one target, and dumping max rank chain heal doesn't sem like a very efficient answer to it. I'm downright irritated by this change, don't like it, and hope they either roll it back or otherwise compensate for it.
That's enough for now. Next week we'll be talking elemental, as I'm hoping to run the Nexus tonight and maybe even Drak'Tharon by the weekend.