Until 5.4, I never realized just how much I resented the way Mists of Pandaria was turning out. I play a healer, and it just seemed like so much of Mists was healer-unfriendly. There was all this neat new content and game modes, and I had to switch to Ret to do most of it. Brawlers' Guild, dailies, scenarios, Battlefield Barrens.
On top of that, it was so hard to gear up my offset, which made doing all this new content even more painful. The loot system in LFR makes you focus on your main spec, so you can't pick up scraps like in a regular raid. All the reputation gear used to cost gold in previous expansions, so I could have bought both main and offset. But now it cost Valor, a much scarcer currency, so all my Valor had to be dedicated to my main set.
Let's put it this way: I entered 5.4 with two i437 green trinkets in my Ret set. And that mishmash was still better than Holy for soloing.
But 5.4 has introduced Proving Grounds, and they are amazingly fun for healers!
My first attempt went pretty badly. Went through Bronze, but wiped out on Silver 5. Then I realized I was healing like an idiot, and decided to play properly. This time I beat Silver, and then wiped out on Gold 5. I spent the next couple of attempts refining strategy, and got up to Gold 9. That's where I stopped for the night.
I really enjoy it. It's not exactly like raid healing, but it is very PvE healing with a little more responsibility for the healer. You want to add a little more damage, stun a little bit, maybe even try to interrupt. As a paladin, you need to use your cooldowns, including Sacrifice.
The thing is that even if Proving Grounds don't teach you to raid heal, they teach you to heal, and to adapt your techniques to different damage patterns (damn rabbit bleed!). If you can do that, learning to raid heal is not all that difficult.
The NPCs are pretty funny, and play just badly enough to make it interesting. They miss some interrupts, don't stack, and stand in the fire. The comments on the healer threads are amusing. Some of the priests were complaining that if they Lifegrip the hunter out of the fire, sometimes he'll manage to Disengage back into it.
I've noticed some interesting conversations on whether guilds should require Proving Grounds for their raiders. I think that requiring Gold is excessive for a normal/Flex guild, but any decent player should be able to handle Silver. Requiring a Proving Grounds achievement is still better than requiring gear or raid achievements. I would break down the levels like so:
Bronze - for people completely new to healing. After this you should be able to do normal dungeons and LFR.
Silver - If you can do Silver, you're ready for Flex or normal
Gold - If you can do Gold, you're ready to try Heroic content
Endless 30 - Probably good enough to hang with the Royalty crowd
I think Proving Grounds is an excellent feature. I hope it encourages more people to try out the group-centric roles of tank and healer. Before Proving Grounds, you had to learn how tank or heal by getting tossed into real situations with other players. While there's something to be said for learning through trial by fire, a lot of people did their best to avoid that harrowing experience.