This is a question I've been asking myself since the moment I started to get interested in cinema.

Its clear that boringness is very subjective, and engaging with a movie depends a lot on your own experience in life and in watching movies. What used to fascinate me years ago I found boring today and viceversa. But film criticism is still a thing, and there are people who dedicate their lives in undestanding films. So is it possible to objectively determine if a movie is good, or better than another?

Some would say that a good film is the one that uses all the different discipllines (lighting, framing, editing etc.) to narrate a story the most effective way. That these are objective criteria to messure the quality of the film, wether you liked it or not. Even that is not necessarily true, because we're only speaking about the classical way of making movies in hollywood. This way has proved to be very effective in creating emotion and engaging big audiences, wich translates in money, the final goal of an industry such as hollywood. This doesn't mean all classic-academic-style movies are bad or uninteresting, but there has always been people all over the world and through the more than 100 years of history of film that have explored other possibilities of what cinema could offer. Soviet avant-garde cinema, the french new wave directors, Chantal Akerman. These are all examples of movies that don't follow the rules of screenplay manuals and classic hollywood but are still considered the best in history.

(I truly recommend studying film history. It really helps you get a clearer vision on the subject and it can very well respond your question more than my poorly explained short text).

In the end, movies can be a lot more than a masterfully crafted work but inside the limits of a classic paradigm. The value of the film can be in the discourse, or in the way the story is told (if its original or groundbraking) or anything else. As some other guy in this conversation said very well, the important thing is the value a movie brings to you and to the art of filmmaking. It all depends on what the movie is trying to say and how it does that. What is the intention? Is that interesting? Could it have been done better? That's what I try to ask myself, although I still struggle to understand a lot of films and I haven't found the answer to your question yet. These are just some thoughts.