I am often astonished how quick Doctor Who fans are to put down this story, while praising its immediate predecessor, City of Death, to the skies. To me they are two sides of the same coin: zany plots, outsize characters, witty scripting (and script-editing) by the incomparable Douglas Adams, and a stellar performance from Tom Baker. And the effects? Well, if one were to believe everything said about the awfulness of the production, one would probably be pleasantly surprised to find that it isn't as ghastly as all that (rather like Weng-Chiang's much-maligned rat). Yes, there are some sub-par shots, but as a whole there is quite a bit of clever artfulness at work - no different from elsewhere in 70s Doctor Who.
On the whole though, I find that the charm and inventiveness of the story wins out over all objections. Lady Adastra is a deliciously arch villainess, and the character of Organon, the canny fraud of an astrologer, is a sheer delight. And what to my 10-year-old self was an excellent primer in economics, remains a superb cautionary tale about corrupt dictatorships that willingly impoverish their people by manipulating scarcity and holding onto lucrative monopolies. Doctor Who at its very best.