This was a pretty excellent listening experience overall. Yes, Once and Future is very much a fan service story.  It's all about the "X meets Y" trope so many critique Big Finish for.  Yet I must say I have largely enjoyed these audios so far.  Two's Company was a little rough but it wasn't even that bad, and then you have stuff like this wonderful little project that I had a lot of fun.

The First Doctor, or, maybe the Tenth Doctor, finds himself on a planet seemingly, but impossibly, recreating War of the Worlds.  It turns out it is all Missy's doing as she too, is experiencing some form of degeneration.  Also, the Paternoster Gang are here, and they are a weirdly welcome and delightful part of the audio.  These characters were always good in moderation up until Moffat got a little too self-indulgent with them.  It's really fun to have the Tenth Doctor interact with the gang and Strax has some very fun scenes here.  I especially enjoy him describing the Thirteenth Doctor as a "little boy with yellow hair."

The real showstopper is Missy though.  Her meeting the Tenth Doctor was something else.  The two have this amazing back and forth and you can tell they are ad-libbing like crazy.  It's so good hearing these two just fall into these old roles and play off each other perfectly.  It easily makes up for the more clunky aspects of the story that turn up here and there.  The doctor remarking how he "wanted to go" at the end feels like an example of said clunk.  It is somehow a cute moment for his character, weirdly satisfying, and took me right out of the story all at once.

I would love for Michelle Gomez and David Tennant to get a box set together because this was something else.