In terms of subverting expectation and critical orthodoxy this was Woody's Dylan goes electric. Anyone who wandered into a cinema to see this because they enjoyed Bananas, would be astonished, and probably felt let down. That moment of shock has never quite entirely subsided.
Interiors is an approximation of classic European theatre, the sort of milieu we expect from Henrik Ibsen. Three sisters (ok, or Chekhov) who work in different artistic mediums are damaged by their childhoods and by their oppressive domineering mother. When their father marries again, each experiences the disturbance of past traumas. The pacing is slowed right down to allow the actors time and space to suggest their emotional frigidity. There is no music.
The exhumation of the internal conflict of artistic and educated upper middle class creatives or intellectuals would become so woven into Allen's films that he would become stereotyped by it. That really started here. Woody's reputation as a strong writer of dramatic parts for women originates here too, with Maureen Stapleton winning a deserved Oscar. This is the first of Woody's ensemble films, a method that would eventually become his standard.
It's easy to accept that some of his audience wasn't ready for this, having already experienced the metamorphosis that was Annie Hall. But it works. For such a sombre and stifling approach it is still gripping, and emotionally convincing.