I did not see the stage play upon which this film is based (too young) but, based on its own merits, this film surely deserves a closer look.
The central trio of performers (Reid, York, Browne) provide career "bests" and there are some amusing vignettes from the others (Fraser, in particular, as a truly odious soap actor).
The much-discussed sex scene is, by today's standards (and, it would seem, even those of the 1960s stage play), tame, but its real value as a display of the shift of power between the three central characters is very neatly worked through in the closing quarter.
The final five minutes of (self-) destruction is heartbreaking, with excellent use made of the music track.
In short: miss it and miss out.