Prior to LK, healers could run out of mana, and for the most part it worked. They didn't just use their efficient heals, because sometimes their group would die if they did. They didn't just use their big heals though, because they'd run out of mana (and then the group would die).When I healed in BC I hated the fact that my HOTs were so underutilized, as they were often quickly over-written by faster direct heals. I wasted my mana but then the Priests who were busy COH healing would always ask (demand) my Innervate on top of it all. The situation was only fixed when I would be asked to tank heal where I'd keep HOTs ticking on the tank but would be using Healing Touch most of the time. In WotLK the situation was much relieved. While my HOTs are still often over-written the "wasted" mana is much less of a concern to me as I have sufficient mana regen to ignore the situation. Regardless I still do considerable healing because I can keep Rejuv and Wildgrowth flowing throughout the raid. In Cataclysm it doesn't sound like I'm going to be able to do that.
I think of healing like a cross-continental road race. If you go too slow, you'll lose the race, but if you just floor it the whole itme, you'll run out of fuel a lot and waste time stopping to fill it up again. There is a happy medium somewhere in between. However the encounter specifics push you out of that medium, sometimes asking you to choose big numbers over efficiency and sometimes vice-versa.
I know it sounds like we are picking on healers all the time, but once you can run out of mana again, I think everything will just feel better, your choices about what spell to cast next become more compelling, and the healing game overall will be more engaging.
I can certainly understand the underlying rationale for wanting to change the dynamic, however I think Blizzard has some gaps to bridge in their rationale and our experience. First, how does any of this change the current healing dynamic where I see virtually nothing but raid frames? I'm able to survive because of raid warnings that tell me to get out of goo and my eyes are constantly moving but that is not much fun at all. I'm not watching the encounter, I'm watching my feet and my raid frames. And it's very much more stressful than either a DPS or Tanking role -- I've done all three.
If there is going to be ample time in combat for these types of decisions to be made, then would this not also necessarily mean that fights are going to be much longer and become more tedious? Doesn't sound much fun to me either. Ask yourself the same questions about PVP and the question just becomes more murky.
All of my questions harken back to what I've said about Blizzard in the past -- that I'm not greatly heartened by the decision making process I've seen Blizzard use over the years. They've implemented too many things to change them too much later on. They've introduced, pulled back, reintroduced and made everyone's head spin in the process. As it is we are to expect almost completely changed game play every 18-24 months and changes that also make such vital roles as healing much more difficult are not welcome in my opinion.