One of the current controversies in the tank world are tanking cooldowns. These are abilities which greatly reduce the amount of damage taken for a few seconds. Though originally created as emergency measures--Shield Wall originally had a 30 minute cooldown--Death Knights were given cooldowns that could be used multiple times a fight. This meant that if a fight had a predictable spike in damage, the Death Knight could line up their cooldown to mitigate that spike, making them much easier to heal.
Since spike damage is generally what kills tanks, this made Death Knights the tank of choice on such fights. The other tanks had their cooldowns improved to match the Death Knight. However, the Death Knight still has the best cooldowns, and is often considered the best tank because of this. Paladin tanks, who only have one cooldown, are considered the worst.
However, two healer classes, Priests and Paladins, also have cooldowns that they can use to mitigate spike damage. Holy Priests have Guardian Spirit, Disc Priests have Pain Suppression, and Paladins have Hand of Sacrifice (coupled with Divine Shield to keep the paladin from dying). Instead of just relying on tank cooldowns, you can set up a cooldown rotation with your paladins and priests to help mitigate damage.
Personally, I find cooldown rotations a lot of fun as a healer. It gives you a chance to coordinate with your fellow healers. It adds a little extra spice to healing, and saving a tank from death with a well-timed use of a spell which is not spammed is fun. Honestly, that's the most fun as a healer, using a spell at precisely the right time to save someone.
Tanks have tanking rotations, where they trade-off mobs. DPS have interrupt rotations, as they trade-off interrupting spells. I think adding cooldown rotations for healers would add a little extra element to the game. It's something more than healing spam, and requires us to work together a bit more.
I think Resto Druids and Resto Shamans should each get a cooldown (like Hand of Sacrifice, etc.) so they too can join in the fun. Then I think that the number of cooldowns the tanks have should be reduced, or the cooldown timers greatly increased so that they go back to being emergency buttons. That should reduce the disparity in tanks, while improving the gameplay for healers.