The worst part about open ratings systems is that the people who choose to rate a movie select themselves. If a million people love a thing, they could be the only million people who love a thing (whereas the OP implicitly thinks of them as the only people who noticed a thing.) And as you say, some things have too large an audience due to marketing. There's got to be some way to offset marketing in ratings by deriving how much was done from the people who chose to rate a thing.
Even worse, a rating could be because the raters were most of the people to notice a thing, but in a negative way. All ratings on the internet about things that center women or racial minorities should be ignored. Because of the overwhelming population of white male (and incel-type right-wing internet subculture) commenters, they can get a hate-boner about a movie or tv show just from the title or subject, network with each other, and then be responsible for an order of magnitude more ratings on the thing than the people who the thing was made for.
I think the best way to find other things you like is to figure out what the authors of the things you like themselves like or have worked on. That stuff is hard to find, though. You can get it from references within the works or from interviews and biographies, but it's nothing that algorithms are extracting yet.
I also find a habit from my old punk rock days to work: find other people who were working in the same place at around the same time. You may actually just like the zeitgeist, but have assigned it entirely to the only authors from that place/time that you've been exposed to.
Critic's reviews I find to be worthless, or at least their text. The ideal critic for me is one that just says "yes" or "no" to a long list of movies. You'll figure out from skimming the list whether that critic is a good critic for you. I often find Ebert's reviews a pleasure to read, but I rarely agree with him about the films themselves. Artistic criticism is generally a writing exercise imo, not anything with an actual relationship to the thing being commented upon. I'd put it 3rd in the ranking of most meaningless journalism, right below sports writing, which is still more meaningful than the ultimate: analysis of the reasons behind today's market movements.