Saw this tonight thanks to TDF. 11th row on the center aisle. A $55 steal.
I love the series. I knew it was a prequel. But, I did not remember everything of the series because Season 1 was 9? years ago. But that didn't impact my ability to follow the story, and it was fun being reminded of things.
The SFX were all pretty cool, and I'm sure it's been said earlier in this thread (which I have not read due to not wanting spoilers), but reminded me a lot of Cursed Child's SFX. That's not a bad thing - I just wasn't as wowed as I think most of the tourist audience was. Perhaps I'm jaded. But it WAS cool.
As for the story itself, much of it was a bore with weirdly aggressive (as in, number of words spoken) writing and a cast that was usually shouting their lines on stage. I'm not sure who in the show is actually young or just playing young but some of those actors...were tough to listen to.
I'm happy to have seen it, though, for the general story (not the random school musical plot within the plot), visuals, and jump scares.