I saw the show off-Broadway in January, and I walked away from that experience thinking Krystal Joy Brown should win the Tony for her performance. She had the audience in the palm of her hand and while, yes, she is a villain of the piece, she was just delectable. You see in the first scene, along with Mary, just how much she's lost and you spend the rest of the show investigating how she got there. When you see her, meek and unimportant in Opening Doors, it all sorta clicks. I found that she, similar to Groff, was able to imbue so much truth to Gussie that I (and everyone around me at NYTW) found it hard to root against her. She was living the same experience Frank was - so if we were giving him a pass, we had to give her a pass, too.
I saw the first preview a couple of weeks ago and found that this is no longer the case. It felt to me like the audience was not on her side. Maybe it's something to do with the loss of intimacy from NYTW to the massive Hudson, but something was off, and it wasn't Krystal's excellent performance. Every line she had, delivered to perfection, was met more or less with groans. And for the most part, I don't think Broadway audiences dislike her performance. I guess they are just looking for a true villain to a piece which has none. All of these characters act terribly at some point in the show, but Gussie is the flashiest and she is not a part of the core four friend group, so it's easy to isolate her and dislike her and view her as the reason that these friends have drifted apart.
All that to say, everyone in this cast (besides Katie Rose Clarke, who I found gave an odd, lost, disjointed, bewildering performance) is giving a career best. How lucky we are to witness this show being handled with such expert care.