tl;dr not a terrible musical and not a bad way to spend an evening but nothing to write home about
I remember seeing a Facebook video of Underestimated which was honestly pretty boring, and I saw that it was the first number in the show in the Playbill, which I thought was a bit of a poor choice. I miss Once Upon a Time from the San Diego tryout, which while not memorable, I thought seemed to work well as both a bit of an I Want song and a vague framing device (I've been saying since I saw it in San Diego that I thought it needed more of a framing device, and they seem to have gone the other way, while just putting a golden frame around the stage). In this version, the paparazzi seems to be both the antagonist and a bit of a looming figure over the events of the show, which doesn't always work. We know the story from the paparazzi point of view already, so the hint of older Diana looking back on her "fairy tale come true" that was in the tryout seemed more compelling to me.
The cast/production value don't disappoint and they've added quite a few new songs in the first act especially, which I think for the most part help move the story along. The music is unoffensive but also unmemorable, but can definitely move a scene along, and most of the songs cover a lot of ground. I thought the opening (Underestimated) and closing (If) were the two weakest songs of the show, with Pretty, Pretty Girl being the strongest. Many of the other numbers are good even if the songs aren't anything special (She Moves in the Most Modern Ways, The Words Came Pouring Out). The main issue, as with other biographical stories, seems to be that there are too many things happening that they want to include and they don't know how to touch on every single thing Diana did without making some things seem rushed and others drawn out.
For those that hated the paparazzi dance (I actually rather enjoyed it before, and it's not dissimilar to the Cursed Child wand dance), there's more of that in this show, though they seem more aggressive and almost exhausting, though there's no doubt it's aged better with Megxit and all. There are a few cheesy lines that still manage to get a laugh, though the best dramatic irony comes from current events and it's unclear whether that's intentional or not (Charles talks about maintaining propriety or else he won't be able to become king). Everyone in my group thought the ending was a bit strange ("weird flex, but okay"
, and somewhat abrupt, but we all agreed that it's not a bad show (on about the same level as Anastasia is what one person said).
Judy Kaye is fantastic as both Barbara Cartland and Queen Elizabeth, and Jeanna de Waal sings her face off as Diana. The rest of the cast is also quite good and gets some features but isn't given as much to work with. Some of the songs end a bit awkwardly, and it's unclear whether there's intended to be applause, but I'm expecting that to get cleaned up a bit through the preview process. The song list itself I'm not expecting to change much, but I really think they could use a new opening especially, and a lot of the Diana soliloquies fall a bit flat.
It's clear that Christopher Ashley knows what he's doing and there are some very good moments in the staging and set, so if you're interested in Diana I'd say it's worth a watch, or if you have out of towners who want something familiar. It's entertaining and worth what I paid (I got tickets on TDF) but I wouldn't go out of my way for it.