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?