Jaws

Well, that was unexpected.  I suspected that this film earned its place on the AFI's list of 100 influential movies by virtue of its social impact, rather than its quality.  And for the first third of the movie, I was comfortable in my assessment: it was a serviceable, but unremarkable monster movie. 

But then they got in the boat.  At that moment it went from being cinematic to theatrical, in the sense of being suitable for the stage, rather than the screen.  In fact, I can easily imagine the best actors of our time being drawn to the roles of three men trapped in a life and death struggle with a force of nature.  Working title: Two and a Half Men (badum tssss). And the movie never backtracked; it never went back to land and remembered that it was a monster movie.  Once those men got in a boat, it became a dramatic character study, and so it remained.