For a mainstream example, take Fast X. It's an objectively stupid movie with a great audience score - because it's exactly what it says on the tin! Nobody is confused about what they're watching. Nobody thinks they're going to get terrific drama or romance or suspense. They're going to get the 9th sequel to a comedy action movie about dudes driving cars.
My favourite way of judging movie quality is checking what kind of movie goers hate it and why.
-Pretentious watchers hating on summer blockbuster movies
-Political things and review bombs
About your specific example Steam comes to mind, they have a great review timeline feature that allows to filter out review bombs.
One feature that would be nice would be a filter to filter out reviewers based on certain criteria
-only one review
-only has reviews on certain films
-account life is less than specific threshold
That DB query is probably too expensive to run on a free site though. An app that scrapes the RT reviews and filters out based on this criteria has been on my list of things to build.