Moonbase 3 is very nearly a Doctor Who spinoff. Created by Barry Letts and Terrance Dicks, with numerous familiar faces and names on the credits, it is set thirty years in the future, a European moonbase in 2003, mainly staffed by Brits with a few comic foreigners, but with headquarters in Brussels, answerable to the Assembly and paid in Eurodollars. Letts and Dicks wanted to make a series with as few counterfactual elements as possible, and unfortunately that really leaves only two plots - crew member puts everyone in danger, or natural forces put everyone in danger. In the first three episodes the crew member who causes problems is a well-known Doctor Who face - Michael Wisher in episode 1, Peter Miles in episode 2 and Edward Brayshaw in episode 3. I am afraid I had stopped concentrating when we had much the same plot again in episode 4, and was mildly wondering how far Doctor Smith, the moonbase psychologist (played by Fiona Gaunt) who seems to have the idea that you cure crazed crew members by snogging them, would be prepared to go for the good of her team.
But the fifth episode, "Castor and Pollux", seemed to me to achieve something rather impressive dramatically. The number three on the base (Barry Lowe, played by Tom Hill - or is that the other way round?), who has functioned as a slightly reticent viewpoint character for most of the series, is in grave personal danger in an incident which combines details of Neil Armstrong's docking problems on his first space flight and the Apollo-Soyuz mission which was then in the early stages of planning; personal and international politics interfere with the Moonbase's planned rescue mission. Because the show had had little compunction about killing off apparently important characters in previous episodes, I was on the edge of my seat yesterday as I watched it on the train. The technical effects are good as well.
Sadly, the sixth and final episode, "View of a Dead Planet", brings out all the series' flaws and more. Michael Gough turns up on the Moon as a venerable scientist predicting imminent doom for the Planet Earth, which indeed appears shortly afterward to have come to pass. I found his character's unpleasantness unattractive and unbelievable, and the reactions of the Moonbase crew to him and then to the awful situation simply implausible and uninteresting; On The Beach it ain't. There is also a nasty sexual assault subplot (analysed in brutal but fair detail here). Writer Arden Winch never did any other sf as far as I know. But it's not all his fault; the whole thing felt frankly under-rehearsed. It is particularly shocking because director Christopher Barry is generally much better (though it should be added that his most recent Who at this point was The Mutants, which is definitely his nadir). I wonder if cast and crew, knowing that the series was cancelled rather than becoming a new grownup Doctor Who, had simply lost their motivation?
Anyway, it's worth watching to get a sense of where BBC sf thought it was going, ten years after the start of Who and five before the start of Blake's 7. (There is one Asian staffer in three episodes, and we see the head of the Chinese moonbase as well; there are a number of women in the team, including one research scientist in episode 3 and Fiona Gaunt's psychologist.) Apart from the fifth episode, I also enjoyed the second, "Behemoth" by John "Colditz/Secret Army" Brason. And you can see them all for free.
Episode 1: Departure and Arrival (9 September 1973): 1, 2, 3, 4, 5
Episode 2: Behemoth (16 September 1973): 1, 2, 3, 4, 5
Episode 3: Achilles Heel (23 September 1973): 1, 2, 3, 4
Episode 4: Outsiders (30 September 1973): 1, 2, 3, 4
Episode 5: Castor and Pollux (7 October 1973): 1, 2, 3, 4
Episode 6: View of a Dead Planet (14 October 1973): 1, 2, 3, 4
Edited to add: I happened to watch a contemporaneous episode of M*A*S*H this evening (2.4, "For the Good of the Outfit", first shown 6 October 1973), and was really shocked by how much better it is.