Basically, five stars is great. Two-and-a-half stars is average. Everything above that is pretty good already. Everything below is not-so-good. Zero stars shouldn't exist or just means that there's no rating yet. Half a star is the lowest rating and absolutely horrible.
I am more lenient with movies that don't take themselves too seriously. On the other hand, I'm more critical about movies that think that they're the shit (Tenet is one example) or those I have high expectations for (e.g. Matrix Resurrections). In the end, a movie should entertain me, which can be achieved in various ways. A good way is to trigger my emotional side, aka to make me feel something. Dune is an example that completely failed me in that regard.
Nostalgia plays a role too, which is why some older ones are rated fairly high. On the other hand, I don't care if it's a "classic" and the general consensus is that it's a masterpiece. If I don't like it then it will reflect in its rating. No Country for Old Men, I'm looking at you. I'm not trying to rate movies to please the masses1.
Sometimes, it takes me several tries to get through a movie. That's usually a bad sign. Even if I don't finish a movie, I may still rate it... badly. Those cases are usually noted in the review.
I try to go into most movies "blind". Movie trailers full of spoilers have ruined the movie experience. Of course, I will have some sort of expectation most of the time, but ideally, I know neither the genre nor the premise and just try to enjoy wherever it is taking me.
I'm not watching movies to try to find where they are lacking, but oftentimes glaring plot holes will completely take me out of the experience. But again, I'm not one of those intentionally looking for plot holes. I usually don't have trouble suspending any disbelief, as long as the movie is well done otherwise.
Since this is a digital garden, things change all the time. Reviews get added, extended, changed. I'm adding old movies I've watched years ago or the one I just finished watching a moment ago.
1 i.e. the three people reading this website