Went to see this at the Phoenix Theatre today.
Definitely the most spectacular thing I have ever seen in an actual theatre that does plays; there's some brilliant effects more akin to an actual episode of the television show, where it's hard to tell what's live and what's been pre-recorded.
The cast are great; remember this is a mostly British cast doing American accents. In particular, the Oliver-nominated Isabella Pappas as Joyce and Louis McCartney as Henry Creel stand out.
The runtime is very long, but there's an awful lot of plot covered during it and it definitely sets up Season 5 very well.
Definitely worth £75, although bring your own cold drinks because they're very expensive in the theatre.
10/10