How much healing is PW: Barrier worth?

Barrier is one of the great new additions for Cataclysm, initially so good that Discipline priests were almost mandatory for much of T11 heroic modes. It's since been nerfed a bit (well, a lot actually) but it's still a mainstay of heroic raiding because encounter design tends towards lots of damage concentrated in short periods rather than being evenly spread through a fight.

So it's good, but how good? Is it as good as Tranquility? Better?