How do you determine if a movie is good?

If I want to watch a movie again within a month, it's a good one.

I know it's good when it leaves a mark on me, and I keep thinking about it for more than a day.

There's not one aspect, but generally I decide if a movie is worth watching by its' reviews on IMDB and Rotten Tomatoes, mainly.

Lately?

If I stick with it.

There really is no other way.

I skim read a load of reviews on imdb .
Bigger dataset than watching 1 trailer , or one pre reviewer

If I enjoy it a lot, enough that I'd re-watch it, and I enjoy it more than I'm bothered by the flaws I find in it. That's it.

If I'm not bored during any part of it.

easy: interest and attention

is it interesting, and does it hold my attention... instead of the usual picking apart the story, production, acting, audio, sets, lighting, camera work.... if I am paying attention to the production, the story interest and attention has failed me.