I am not sure what I think about having three different single target healing spells: 1,5 second cast, 2 seconds cast and a 3 seconds cast. I have to say that Blizzard is right that healers should think more about their mana pools than now, but I think it's a wrong way to achieve it.
I can see when a fast small heal is effective, and I can see when a slow strong heal is effective, but I can't see why you would want something medium. I can't imagine an encounter where all three will be needed in order to have a balance between mana and healing output. Yeah, it sounds logical, but when I try to imagine it, I just can't. Then the 1,5 heal need to be very small if a 2 sec has to be more effective, but if a 1,5 sec heals too less, it won't save lives for those "SPAM" situations which they try to explain it's meant to be for. I'm sorry I just don't see it, but perhaps it's because I'm not used to the increased healht pools or something.