The reputation of this performance is not good. The initial reviews were quite scathing. The competition from the Johnson/Suzman/Nunn version is decisive; the other version is better. However, there are many fine things about this video. Let's talk about them first.
Ian Charleson's Octavius Caesar is good, a schoolmaster with ice water in his veins. Many of the supporting players are quite fine. The almost completely blind Esmond Knight does a hilarious drunk scene as Lepidus, and Donald Sumpter gives Pompey a model reading.
The visuals are spare but more lushly colored than usual in the BBC series, giving a Mediterranean vividness to the whole show, even if lovers of spectacle will do better with the Taylor-Burton film.
Emrys James is less successful as Enobarbus. This part is generally considered actor-proof, but here James is charmless and without variation. His great speech describing Cleopatra's barge is completely ineffective. Whether the blame is his or the director's is lost to history, but I'm betting on Jonathan Miller's expressed annoyance with "tired" tradition.
However the real problem is with the two title characters. It's as if you'd gone to the theater, settled in your seat, and then heard an announcement that owing to the leads' illness, the actor playing Enobarbus would instead be playing Antony, and the actress playing Charmian would take on the role of Cleopatra.
Colin Blakely was a bright spot in many fine films during his career, but they were usually other peoples' films. Here he understands the character well enough and gives a good performance. He plays all the right notes, but he himself is the wrong instrument. He's simply not an Antony.
Jane Lapotaire is a bigger problem. Her portrayal of Cleopatra is small to the point of cramped, mechanical, calculating, and self-obsessed. A shopgirl's idea of a queen, she never strikes a single true note. In the first half of the play, she's merely wrong. In the second half she becomes an active trial for the viewer. When Antony is finally dead, instead of rising to greatness in understanding, she shrinks into dreary, unspontaneous hysteria. This is one Cleopatra who learns nothing from her experience. While she goes on and on shrieking and weeping, you wind up urging the snake to get on with it.
So it's not an out and out disaster, but with the poor casting of the two leads, the show never quite pulls itself together. Turn your attention immediately to the RSC version with Johnson and Suzman, and don't look back.