^ Surprised to read this, I must admit. Sienna was so bland as Sally it was almost as though the show didn't have one. Her singing and dancing were passable, but nothing -- nothing -- made you look at her as opposed to the ensemble. I'm not suggesting she needed to be a great singer or dancer, because Sally obviously needn't be, but she needs to have a drive to command your attention, and she did not have (or earn) that for a second. Her book scenes were fine. No more, no less.
The video clips I've seen of Emma Stone all suggest a better performance.
But I saw both women interviewed together at one point, and they both said they got sick during the rushed rehearsal period and didn't feel on top of the role until they were ready to leave. I saw Sienna around two weeks into her run. A week or two later, I might have seen a very different performance.
Michael Halling is an excellent actor/singer. I would love to have seen him as Higgins, but, dear God, yes, that first performance must have been one hell of a pressure situation. He's up to it, though. He's been great in everything I have seen him in.