Undoubtedly, the Marvel movies are very popular. But lately people have conflated this popularity with some amazing quality in the movies, and have pushed to have it recognized as great cinema. But this is a flawed perspective. These movies may be popular, but they're not amazing works of art. In fact, it's precisely because they're engineered to be popular, to be blockbusters aimed directly at entertainment, that they're disqualified from such recognition. Of course, the Marvel movies are adaptations of comic stories. They're about good guys beating bad guys and saving the day. It's the perfect escapist, action-adventure diversion for a weekend at the movie theater. The glamorous action, shiny costumes, simple moral lessons, and even the quippy humor make them perfect family watches. But they can never be truly great, artistic films; they're just too superficial to do so. The Marvel movies aren't bad, per se. They do what they're supposed to do well. And what they're supposed to do is provide easy entertainment. But they're not great artistic works. They're not supposed to be great cinema, and they aren't.
Marvel is certainly entertaining, funny, and family-friendly. But to say that that's all it is misses so much about what makes it good. The MCU follows engaging arcs of complex, interesting characters, and touches on very sensitive subjects, such as racism, government control, PTSD, patriotism, and much more. Along with the factor of spectacle, Marvel filmmakers commit to telling genuine, compelling stories.