Personaly, I'm not a fan of the 12 second change to it. It's annoying, boring and still leaves the sheild confusingin it's purpose.
I would much rather see a massive mana drain sheild, a mana regen reduction sheild, partial damage reduction sheild or anything that adds to the gameplay more then the 'this is absuable, lets make it switch off every X seconds' which honestly still leaves it reallly darn powerful.
if that time was a lot /lower/ with a fixed mana cost, it would feel a lot more like the intended short block it was.
Definatly needs some work and expansion at some point. They look like a great way of making gameplay more varyed,