1. Too much CC (especially instant CC)
There's too many different kinds of CC and it all lasts way too long. PVP is not fun when you can't control your actions for more than half of a fight. Abilities that take away control should be powerful, but not plentiful.
Shockwave and (Blood) Fear are certainly the two biggest culprits, but there's also Fist of Justice, cat Cyclone, Typhoon, Deep Freeze, Disorienting Roar, and Intimidating Shout, to name just a few. They're all fine abilities in a vacuum but when you consider the impact of chaining them together and how short their cooldowns are then it just makes PVP a very frustrating experience. The game needs less focus on taking player control away because it leads to...
2. Too much burst, both damage and healing.
It's not fun to get a healer (most notably, a Shaman) down to 10% health only to see them instantly crit heal up to 90%. It's also not fun to watch somebody take 80% of their health in a single Deep Freeze or die from 60% health to a 5stack of Taste For Blood.
The reason healing has to be bursty is because CC is so plentiful and lasts so long. If a healer only has 1-2 seconds to react to spike damage before they get hit with another interrupt, silence, stun, fear, etc. then that heal has to be strong. However, if we tone down CC then we can smooth out healing since healers will have more time to deal with incoming damage. Damage has to be bursty right now because healing is bursty because CC is so plentiful - it's a horrible snowball effect.
Most classes have several cooldowns that they all stack ontop of each other to maximize burst because getting a kill otherwise is nearly impossible. The "swifty one-shot macro" is so popular because there is no downside to stacking all cooldowns on top of each other. Outside of these cooldowns damage is pathetic so the game is encouraging you to stack them.
DPS doesn't need 2-4 burst cooldowns. Remove spells like Holy Avenger and make Sanctified Wrath a 2minute cooldown - this makes burst windows available more often but less threatening each time. Sitting around for 3 minutes to try and set up another kill is boring.
Once you tone down the ridiculous amount of control that everyone has then you can make healing less bursty, which in turn means that damage can be smoothed out, and people can actually survive without being at 100% health all the time.
3. Too many defensive abilities.
Because damage is so spikey and healers get precious little time to actually cast, everyone needs some defensive skills. Unfortunately, we have an oversaturation of them right now, especially when you also look at using CC defensively and hybrid healing. If you make CC less plentiful, you can tone down burst healing from healers, which means dps won't need so many defensive cooldowns.
Nothing can change unless you tone down control of every class. Hammer of Justice used to be a powerful ability but it just doesn't hold a candle to all the new control options in the game. I don't want to play in a world (of warcraft) where Fist of Justice is a mediocre stun.