This spec has definitely been a game-changer; it's either too good or too bad, and right now, it's definitely too bad.
I think this is due to the fact that the class already has a healer spec and a damage spec, and trying to merge them somehow is unfeasible, based on the various changes made.
My opinion is that the shield spec should be a tank-type spec.
It would need Taunt/Skill or armor/Aggro tactics and some CC.
This is just a macro view of the idea, but I think it would be interesting.
The skills and behavior of everything need to be studied to make it work properly.