I don't know enough about Equity's rules to speak on how Gold was allowed to perform, but it was definitely unexpected. First off, congrats to all of the understudies who made this show happen tonight. It was clear that there was a lot of scrambling and shifting of parts in order to do the play. For reference, Danny Wolohan was on as Duncan, the Porter, and Seyton. Stevie Ray Dallimore played Siward. Peter Smith doubled as Malcolm and the Bloody Captain. I could be wrong as I haven't seen this production previously, but I believe Sam Gold was on in the Lennox/murderer track normally played by Michael Patrick Thornton.
Performances - Ruth Negga as Lady Macbeth is the standout performance here. I thought she was particularly good before intermission where frankly she just has more to do. Daniel Craig was surprisingly nuanced in a couple areas but, bafflingly, made the role much more comedic than I've ever seen it played. Amber Gray was strong as others have noted. The idea of Banquo as a mother who cannot be king and yet will get kings is an interesting concept, but I'm not sure they've gone as far as they could exploring that dynamic.
Overall thoughts - I liked this production more than I liked Gold's King Lear. But I detested that show, so not a very high bar. I'm a huge fan of the play itself, and being extremely familiar with the text, I didn't have problems understanding what was going on or who was who. However, I completely understand how someone who didn't know the play would get lost. There are many instances where a cast member exits in one role but comes on in another without any real signal to the audience that we are now seeing a different person. Some change in costuming, etc. might help with that. That being said, the visual look of the production didn't bother me. I don't have a problem with the modern dress or lack of big scenery. Funnily enough, I thought Gold fit right in with the rest of the cast in his street clothes. The problem is more that the world of the play that Gold has created does not feel cohesive. They're just throwing a bunch of ideas at the wall and seeing what sticks. Cook soup onstage! Throw in some fog machines! Now we'll blast the audience with some bright lights in their faces (which happens quite a lot by the way)! There are some moments that really work and are exciting, but they're unfortunately few and far between.