Over the years of my playing WoW it has been easy to see the yo-yo of classes; one expansion beast master hunters are garbage, then the following expansion they're wrecking machines. I used beast master as an example, because I toiled through Cataclysm on mine against the advice of everyone and am absolutely shocked about their dominance in MoP.
It's a regular thing in battlegrounds for my hunter not to die and rack up 10-15 kills. Last night in the Temple of Kotmogu, my hunter was taking on 2 or 3 enemies at a time and stepping away victorious. It's almost too easy. On the other hand, my boomie is a glorified practice dummy. Boomies have no stuns, no pets (unless you spec for treants), and 2-3 second casts which require them to stand still to fire off. Usually I have to run away, root, kite, spam moonfire/sunfire (I hope to proc starsurge during this and wait for starfall to come back up) and heal myself--it has terrible mechanics. Compared to both my hunter and frost mage that have silences, stuns, roots, superior defensive abilities, and ways to break out of CC it's a downright travesty.
For certain classes that were either nerfed into oblivion or are underpowered, PVP simply isn't fun. It contains a handful of the same problems as in Cataclysm: MMR exploits, unbalanced BGs where one team is stacked with healers and the other team has none, as well as teams loaded with fresh 90s pitted against a team loaded with fully PVP geared players, raid gear boosting dps classes, and flavor-of-the-month classes. There are definitely specs that need buffs to bring them to the level of others. Boomies, in particular, need their instant roots back (it made a world of difference); I really don't understand why it was removed to begin with when most classes have instant roots like a mage's aoe root, frost nova.
The state of crowd control is obscene. There's simply too much. If outnumbered, a player must be lucky enough to run away. Otherwise, they'll be caught with a chain of CCs and stare at their PC unable to move until they are dead. When that happens, especially if your trinket is on cooldown, no amount of gear or resilience will save you. I don't even know if it can be called playing; it's more like watching a video.
One thing Blizzard somewhat fixed was the ridiculous survivability of healers. The mana cap plays a large part, as does the abundance of CC and the burst damage that a few classes now sport. Even in arena, it's a noticeable difference from Cataclysm. Healers these days don't feel like boss fights.
Their attempt to even the field with baseline resilience hasn't been that impressive. If a player doesn't craft all or most of the PVP gear when they first hit 90, they're fodder; even with that gear, other players will stack PVP power gems on their honor gear, which bypasses the resilience. The end result is really no different than Cata; I've actually seen characters die faster this xpac than in previous ones, yet once fully geared, my hunter feels tankish against everyone but those that outgear me.
What I have talked about, the biggest problems, were addressed in a Dev Watercooler by Ghost Crawler, and I feel if Blizzard follows through with what he states there's a good chance they might actually balance PVP this expansion--might. The one issue that remains, which GC seemed to be content about, is CC. I really hope they one day make it so all CC used on a player diminishes the way fear and cyclone do. For example, if you're frozen, then someone fears you, the following CC doesn't last as long. I also hope they stop adding new CCs to the game. There's more than enough already.