I had never heard of this film, so I didn't know what to expect. I figured that anything featuring Attenborough and McGoohan had to be good...and I was right.
The film begins with preparations for a big jazz party honoring Rex and Delia's first anniversary. When they walk through the door, we get a big surprise: Rex is black and Delia is white. (Mixed-race couples were rare on screen in 1962, although they're now "de rigeur" in British TV and film.) When McGoohan's character started his scheming, it finally dawned on me that I was watching OTHELLO in a warehouse!
The screenwriters did a decent job of condensing Shakespeare's play into 90 minutes and bringing it up to date, but they chose to change the ending, which may disappoint die-hard fans of the Bard.
What makes this movie stand out is the cast of supporting characters: great jazz players of the early 1960s. The three headliners are Dave Brubeck (playing "Unsquare Dance"), bassist Charles Mingus, and sax player/bandleader Johnny Dankworth. But there are many second- tier players who contribute to the swinging atmosphere.
This film would be of interest to students of Shakespeare, or lovers of jazz. And if you like the idea of a "jazz summit" in a film, also check out A SONG IS BORN, a Danny Kaye comedy from 1948. The jazzers outshine the actors in that one; in ALL NIGHT LONG, it's a dead heat.