I saw the second preview too (thanks again call_me_jorge for the ticket!!) and I pretty much agree with him. The performances are all fantastic (David Schlumpf as Dan in particular stole the show for me), but the staging needed tightening. There were sight issues. Really the only big set piece that moves is an L shaped piece of wall with a bookshelf that comes on from time to time, and there were times action was happening on the other side that I couldn't see. Also, at the beginning of the show, Natalie is playing on a real piano, but at her recital, it was mimed (probably because this happened on the upper level and they couldn't get two pianos). Also, at the very end, Diana, exits through a very big, very prominent sliding door at the back of the stage, and it felt very underwhelming. I was staring at this door the whole show, thinking "Oh man, when someone walks out that door, my jaws gonna hit the floor", but she just slid it open a few inches and walked out. Kind of a let down.
That being said, I'll reiterate that the cast is great. I actually liked the slow, droning Dr. Fine. It kind of had a dry comedy to it, and it makes more sense why Diana would get lost in the medical jargon. Henry is an old classmate of mine (graduated when I was a freshman) and it was great to see him perform again. Natalie was great, and seeing her breakdown during "Catch Me I'm Falling" broke my heart. Diana did great work, even if it felt like she was mimicking Alice Ripley at times. Gabe didn't hit all the notes, but he had a nice charm to him. David Schlumpf was my favorite part of the evening, probably as Dan. Watching him slowly be broken apart by grief over his son and his wife's drifting away was gut-wrenching. There were some really cool moments with the staging (particularly "Wish I Were Here", including some really cool lighting design with flashlights), and I really like the show being performed in such a small space. It befits the naturalistic elements of Next to Normal to see it so up close and personal.
Also, Gabe does a Fortnite Dance. That alone is worth the price of admission.