Devs I must say I am very pleased about the update to shield mastery. It appears to be work very, very nicely. Just running around Amarath it gives a sense that AC has some meaning again. My only objection is that you didn't do anything with improved shield mastery. I know there has been a discussion in a few other threads regarding this and I feel it is definitely something you should consider.
To be honest I wouldn't even mind a small reduction in shield mastery and then getting that reduction added back in with a bit more of an increase with improved if that would work to balance things out a bit more.
Again nice job