There's two big, spectacular moments in Act II:
Firstly the snow. They've gone all out, it comes from all directions and literally fills the auditorium. I couldn't see of course, so could be wrong, but I have to assume rear orchestra is not hit by it directly and I'd think that would be less fun. It's a really joyous moment.
Secondly the moving dinner. When Scrooge takes his nephew's feast to the Cratchit's it's done from all over the theater, with performers everywhere, (fake) food coming in from all angles and levels (they even had little vegetables parachuting down) and involving many audience members, culminating in a giant turkey on a zip wire from the back of the mezzanine. It's the sort of moment that could be schmaltzy but in an otherwise darker show they absolutely nail it.