What makes a good film? Couldn’t tell you. A bad film? Well, I could hazard a guess: inauthentic writing, directionless acting, perhaps disorientating editing. But I’m not convinced that one can pinpoint precise technical lack in such a specific way, certainly not genetically.
A good film, by its very nature, has good sound (and perhaps this is true across the technical and creative departments. I’m only singling sound out because it’s what I’m most interested in, and know most about). Could you name a good film with bad sound? If a film is good, the sound must work in service of that which is good. Bad sound can’t work against the good qualities of a film and that film still be good. The power and impact that sound has on a film is too great. This is dependent on genre a little bit, though. The big, brassy type of films are more dependent on a certain sound aesthetic and, as with any film, the sound must 'fit' - be appropriate - for the genre and the context. All this is to say that a film may be able to get away with terrible dialogue, but a flat soundtrack doesn’t reach the threshold above which one is able to believe in the film as an artefact.
To end, I would say that incredible sound will not make a bad film good, but good sound will make a bad film watchable. Which is all one can really ask of film sound in challenging situations.