* If tomatometer & audience score are within 5% of each other, you can trust the ratings to give you a decent indiciation of movie quality.
* If tomatometer is more than 15%+ higher than audience score, it means it's an artsy fartsy movie that critics like and movies don't.
* If audience score is 15%+ higher than tomatometer, it's a fun movie even if it's not oscar worthy. (https://www.rottentomatoes.com/m/old_school is a perfect example)
80% fresh means that 80% of reviews are "positive" it's not 8/10 how some people like to think.
I would much rather watch a movie that has a 50% on RT and a 70 on Metacritic than a movie that has 100% on RT and a 70 on Metacritic. I might not like that 50% movie, but those ratings show some people really love it. The 100% movie's ratings show that everyone kinda likes it, but few people feel strongly about it meaning it is probably not a very interesting watch.