* 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)
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The Last Jedi
Tomatometer 91% Audience 41%: Artsy Fartsy
[Really?]
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The Greatest Showman
Tomatometer 56% Audience 86%: Fun, not oscar worthy
[Won Oscar for Best Original Song]
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EDIT: Truthfully, it was the release of these two films (both Dec 2017) that caused the Tomatormeter and I to part ways. Simply indefensible, IMO.
Oscar worthy - best picture, best actor, etc. Best original song isn't a top tier category. That year also had weak competition.
The Greatest Showman was nominated in a single category, and it lost to Coco. I don't know where you got that it won. Coco got nominated in two categories, one of which was important, and won both. Coco also within 3% difference on rotten tomatoes.