I have played each heal class at least to some extent. Though my shaman is still at 60 and my paladin is 83. I think each class has its fun parts and drudgery.
The main thing has to be that I can do damage while I heal. Granted it isn’t that great of damage but it is more than most healers, even Shaman with their chain lightning (though not as mana friendly). I like being able to Power Word: Shield and start casting holy fire/smite to do damage until someone’s health drops then it is generally penance to full and continue holy fire/smite (mainly in dungeons). I like to be actively doing something. I’ve played classes where the only time you were hitting a button was when it lit up (looking at you level 15 pally). It was frustrating and boring. Give me something to push and I am happy.
The damage I do also allows me to stay in my heal spec to do quests. On both my Paladin and my Druid I had a rough time trying to quest and kill mobs that were yellow to me while in my heal spec. It just took too long and was frustrating. Both cases I’d switch to my tank spec and have a much easier time. Granted it is easier to do some questing in my shadow spec but I can efficiently kill things in my disc spec.
I also feel for the most part that I can be effective in any fight, other than 2 healing spine. I go out of mana too fast on that fight since the majority of the “healing” is not something you can prevent which is my strong suit as a discipline priest. Most other fights though I have a tool that will work for it. Chimera, binding heal is superb, Madness barrier and power infusion help to get those heal intensive parts down.
I’ve not found a heal like Penance on another healer class/spec. A channeled heal that also works as damage that looks really cool while it spirals to your target. It is an awesome heal that does significant amount of healing. It is just plain fun.
The original thing that drew me to discipline healing was the bubbles. I love Power Word: Shield. I was sad and confused about what a discipline healer was when at the start of cataclysm they made it so mana impossible to bubble spam. I loved the Lich King fight spamming bubbles on everyone in the raid. That fight was awesome for my bubbles (the fight was just plain awesome too). I remember doing LK when 4.0 dropped. The week before I healed it like no ones business with mana to spare at the end, then 4.0 and I was oom a minute into the fight. I was at a loss at the time for what to do and how to heal.
That is the main reason that I am never too worried now with the changes in Beta. I know that no matter what, I will figure out a game play that I enjoy and that will work. Blizzard wants me too. They want us to keep playing and aren’t going to completely kill one class or another, no matter how much it seems like all the whiners say different.