Movie ratings from Rotten Tomatoes or IMDB or another site will always have exceptions where the rating doesn't match one's perception (after watching). But they give something to start with when deciding whether or not to check out a movie or read further about it and/or watch trailers, etc. That "initial push" is what I rely on these sites for - in other words, they help indicate whether a movie is a dud or not.
For me, the Rotten Tomatoes rule of "60%+ approval as fresh" doesn't work quite well. So I rely a bit more on IMDB ratings and the top reviews. If I had to rely only on RT, I'd have missed many movies that I personally enjoyed (sorry, don't remember the names/ratings).
As a rule, I usually avoid anything rated below 5 on IMDB, but I do like checking some movies out for the cast, even if the story, script, direction, editing, etc., are awful. In fact, looking at the cast is one of the ways I look for movies, and I sometimes binge watch one particular actor's movies to catch up with older ones that either weren't super hits or were made at a time when the actor wasn't yet well known. Those are usually so heartwarming to watch and get the breadth and depth of the actor's capabilities and also see how they have grown or changed over time.
There are also differences between how some movie critics, with a lot of knowledge and deep appreciation for certain aspects of movies and movie making, look at and rate a movie vs. how an average person (like me) would. Many people just want to be entertained when they watch a movie or show. There are fewer, in proportion, that have high standards for all aspects of movies. Even many people who claim to be "movie buffs" or write movie reviews on their personal blogs aren't as stringent. The masses need a more balanced view between what's strictly critical and what's strictly sheer entertainment value.