The O2 has heard some ear-bursting screams in its time, but when Jane Lynch -- aka 'Glee's Sue Sylvester -- appears to kick off this show, the reaction is up there with the best of them.
What's funny, though, is that Lynch's appearance is no more than a prerecorded message on a screen. When the actual cast of the programme appear in the flesh, the howls make you wonder if you'll ever hear properly again.
It's an emphatic reminder, as if one were needed, that 'Glee' is beyond huge. It has a subculture all its own, with slogans, in-jokes and hand gestures, and it makes grown-ups cry with excitement. No mere telly show in the last decade can touch that.
Once the talking is done, the crew kick off with Journey's Don't Stop Believin' -- their first hit in 2009, off the programme's cross-platform assault on pop culture. An irritating song, but it's a wise choice to begin the affair. When the crowd are on their feet one song in, you've got half the battle won.
The dancing, the singing, the joking, the high-fiving -- there's an enviable sense of ease about the way they take to it all. But is that enough?
As a closet fan -- well, until now -- I'm one of many who holds the show dear for its dark take on high-school life, its sharp dialogue and the depth of its character ensemble. None of those elements are in the O2 tonight.
Instead, we have just songs. And more songs. Then a pre-recorded message from Will Schuester (Matthew Morrison), an awful attempt at 'live' dialogue with one of the on-stage characters. Then more songs.
It's quite like a lowlights package of the series; the bits we'd fast-forward through if we could. Any 'Glee' cynics dragged along tonight will leave with their viewpoint enhanced: This is 'High School Musical' for slightly older teens.
To add to the disparity between stage and screen, leading lady Rachel Berry (Lea Michele) fades into the background. Although Mercedes (Amber Riley) and Brittany (Heather Morris) fill the void adequately, there's no escaping the feeling of a half-baked 'Glee' experience.
Still, a live dialogue section between Kurt Hummel and Blaine Anderson (Chris Colfer and Darren Criss) restores some of the in-universe charm, and a richly harmonised version of Queen's 'Somebody to Love' makes for a rollicking finalé.
Plenty to be gleeful about -- but far less enjoyable than the 'real' thing.