What is a good movie?

First, a good movie is audiovisually impressive. A movie is not a novel. If you cannot remember a scene from a movie, it is unlikely to be a great movie.

Second, they are not boring. Unlike when you read a book, you cannot control start, stop, or pause watching movie. Yes, you can with DVD, but I am assuming a theatre experience. Unless it keeps your attention throuout, it is not a good movie.

Finally, they have a value proposition. A value proposition of a movie is "why you should see this movie." It could be a good story, a strong message, or a very impressive visuals. A movie does not necessarily need a good story, although it would certainly help to have one. A movie has many ways to be 'good'.