A movie can be "great cinema" without attempting anything more audacious than pure entertainment, but what makes these movies fall shy of that is a certain genericism to the execution.

Michael Philips, one of the other critics up there, articulated fairly well what's wrong with these movies as works of cinema:

...the chief limitation with “Endgame” relates directly to how the Russo brothers approach the staging and composition of pure action... with so much of “Endgame” taken up with two- or three-character conversations, things occasionally become stilted because the camera doesn’t interact with the actors in any fluid or striking ways.