It is true that masked acting, done well and in an appropriate space, is very effective. The Tom Patterson Theatre, which features three-quarter seating around a long rectangular thrust, is much smaller and more intimate than any Greek theater. And while William thought that his actors took to their masks quite well once they got used to them, I spotted only two whose masks were truly their faces and not appendages on their heads - and those two were members of the chorus. I found myself watching them rather than the principals, because they were simply more interesting to look at. Of course, once they had got rid of their long grass skirts, the chorus membres were free to move their bodies in a way in which many of the other actors were not.
Masks demand large gestures, or at least definite gestures, concentrated, energetic movements.
Pentheus and his followers were too tightly bound in cloth to make any such movements, and so their masks were flat and unexpressive, their performances static. It was often hard to tell who was speaking. The production was further marred by an excess of special effects, expenditure to no purpose other than trivialising the show. Euripides had very little in the way of special effects, and had to create the mood of his productions in broad daylight, with acoustic instruments, relying on human beings to make his play work. Stratford's actors are trained and talented, and by boxing them into their costumes and overshadowing them with lights and electronic noises, William did them a disservice.