Overall, big fan of this episode. I had a lot of fun with the various alt-universe characters and it sets up the series finale to go as big as possible.
I see mostly people agreeing with the point Boimler makes about how multiverses are typically a bunch of rehashing, and I am more of the same. There is a rebute given in the episode: There's so much new and interesting stuff that is possible in other universes. That might work within the narrative. However, as a comment on the use of multiverses in fiction, it falls utterly flat. We don't get a Star Trek parallel universe show with all new characters and concepts, because at that point it is just a different show that is either weirdly disconnected from the rest of canon or, even more weirdly, not Trek shaped. The "infinite possibilities of imaginative things" is just all of fiction. Multiverses in media are necessarily rehashes of characters and concepts, because otherwise they would just be new universes and not multiverses of that thing.