I think the new cast does a wonderful job, with two exceptions. Even the new ensemble members are great (is that what we call them even though this is a play and not a musical). Unfortunately, I'm not impressed with either Jenny Jules as Hermione or Bubba Weiler as Scorpius. There are some good and and not-so-good things with Jules's portrayal, so perhaps she'll find her rythm. It was the first performance, so I can be a bit forgiving while she discovers what works and what doesn't. However, Weiler is giving a not-so-impressive performance as Scorpius. He is definitely taking a different route with the character than Boyle did, but we lose a lot of the laughs as a result. I also didn't see any real chemistry between Scorpius and Albus, so it rings "forced" when they fight and then make up (and the staircase ballet falls flat). Hopefully the two actors will rectify that as their run continues and they begin to trust themselves more. When I first saw the show in London, with a replacement Scorpius, the actor was definitely modelling his Scorpius on Boyle's. Since Weiler seems to be deviating a bit, he needs a little more time to develop it.
I also wasn't a big fan of the new Draco, but that's because he just doesn't "look" like the Draco I think he should look like. He "reads" older on stage than Harry, so that threw me a little as well.
Line deliveries were faster last night, and I attribute that to the first performance jitters I'm sure many had. The pepper imps effect fizzled out, the cast seemed hesitant in the "transition" from Kings Cross to Platform 9 3/4, and the kitchen duel seemed slower.