The most interesting change about healing in my mind is that you really are in less control of the situation then you were before. In WotLK you pretty much spammed heals the whole time. If you fell behind in your rotation, goofed up, got lag, decided not to heal someone, it was over pretty fast. You had a lot of control over the situation; assuming you were fast with the face-rolling.
Now things are pretty much out of your control. People die because they take too much damage, and there's little you can do to heal them back up. There seems to be very few things that will one-shot people; and those that can are avoidable/interrupt-able or something. Now the emphasis is back on the other members of the group. You're there with your finger in the **** praying no one pokes more holes in it then you have fingers.
Now its more of: how long can I make my mana last while keeping everyone alive? I don't know if I like the loss of control over the situation, but I really wasn't a fan of having everyone 1.5 seconds from death at all times in wrath. I mean, its nice to know if I have a lag spike, people will still be there when I get back.
Also, if you are doing 5-mans and/or aren't going to swap your innervate with someone (and hence don't need the glyph), an instant cast Entangling Roots is a lot more mana efficient then throwing heals on someone. It's only 7% of base mana, compared to RJ which is 20%... just food for thought.
Edited heavily for clarity
Edited, Jan 27th 2011 9:34am by someproteinguy