There’s about a million factors that go into making a movie good. I could spend all day and all night naming them - mise en scène, thematic message, interpretation of genre tropes - and I still wouldn’t be close to done. All of these are interesting critiques, and when you hear an expert discuss them it can be incredibly insightful, but as a layman it can be difficult to even express why we like certain things. And while a broad strokes review is still more informative than a number out of ten, with the increasing prevalence of shorter content and shorter content about content, why not settle on a more effective rating scale.
A four star rating system isn’t some game-changing innovation but it is a nicer system than rating things out of ten (and to a lesser extent, out of five). The problem with those systems is that they’re not very interpretable. Someone’s 5/10 may be another’s 7. When there’s so much choice people tend to not use the extremal ends of the spectrum, knocking off points for problems they never even considered until asked to rate it. All this contributes to the seas of sevens we see on IMDb. The Rotten Tomatoes score does much better here as they use an even coarser binary scale of whether a critic liked a movie or not, and use the wisdom of the crowd to average them into one neat score.
Since you probably would like to signal to people with at least some degree how good something is, I find a scale out of four (no half points) is a good tradeoff. Most people’s ratings will be easily understandable, with a 2 for something like an average or just fine work, and a 4 for something’s that’s one of the best in class. If words elude you consider a number out of four.