I don’t know anything about Pokémon, but my kids are into it, and so I’ve been checking our reviews of the new Detective Pikachu movie. The reviews from Pokémon fans are quite good. The negative reviews largely complain that it’s inaccessible to people unfamiliar with the source material. Along similar lines, one of the few consistent complaints in reviews of Avengers Endgame is that it’s a movie loaded with fan service.
This sort of criticism strikes me as odd. Why should we expect that cultural artifacts must be entirely transparent to people without knowledge of their context? So much of our cultural output is now embedded in richly imagined worlds with long and complex histories. That’s a great part of their appeal to fans. And while it makes sense for franchises to offer starting points for the unfamiliar—to provide good places to start developing familiarity—it’s unreasonable to demand that every entry play this role. Esoteric entertainment is tremendously entertaining for those initiates into its details, and it’s okay that the entertainment industry occasionally or even frequently produces esoteric entertainment. There’s so much stuff produced, after all, that you can always find something else to watch if this particular movie isn’t meant for you.
I imagine Detective Pikachu would be a good deal less fun for Pokémon fans if it spent the first twenty minutes telling you what Pokémon are or if it had an exposition dump every time a new pocket monster showed up. And Avengers: Endgame is the series finale of what amounts to a ten year, high budget TV show. Of course it's going to be about what came before, and of course it's not terribly worried about the needs of viewers who haven't seen the twenty plus episodes that came before it.
Noting that a movie is inaccessible to newcomers is fine, and a movie review ought to note that. But it's awfully weird to see reviewers say a movie is bad because it assumes prior knowledge or is targeted at people who already love the fictional universe. Our creative culture is rich enough and with enough variety that we can cater to different tastes.