It has sometimes been suggested that Doctor Who is at its best when its roots are showing. Those who hold that view would no doubt find much to admire in Underworld. 'Bob Baker and Dave Martin's second [story] for the fifteenth season... is one of a long line... with an uncredited extra author,' suggested Andrew Martin in In-Vision Issue 28, dated November 1990. 'In this case it is not the script editor or another trusted, experienced writer but the generations of Greek storytellers who created and refined the myth of Jason and the Argonauts. While stories such as The Brain of Morbius are reworkings of classic tales of literature under greater or lesser disguise, Underworld is an instance of a story owing so much to its roots that the authors feel obliged to acknowledge the fact in its closing moments: "I called Jackson 'Jason'?... Jason was another captain on a long quest."'
It seems obvious that writers Baker and Martin intended the viewer to realise at an early stage that their story was based on Greek myth, and to take delight in spotting things like the similarities between names - Jackson/Jason, Herrick/Heracles, Tala/Atalanta, Orfe/Orpheus, Minyos/Minos, R1C/Argossey, P7E/Persephone, and so on - and the parallels between the Minyan race banks and the Golden Fleece sought by Jason and his crew. This actually works rather well, giving the story an extra level and lending the whole thing a mythic quality.
Underworld is however a story that has had a generally bad press over the years. The following comments by Howard D Langford in TARDIS Volume 3 Number 3, dated May/June 1978 are fairly typical: 'Underworld I thought was a terrible story, with virtually nothing to recommend it. The first episode was very tedious, and the plot in general seemed very weak. The sets were bad, the acting was bad, the script was bad. There was far too much reliance on weapons. One of the most important characteristics of the Doctor has always been that he never carries a gun, but uses his wits to get out of tricky situations. The coming of K9 is a curse which has changed all this and has worked for ill on both the originality of the scripts and the fame of the Doctor as a moral agent who disapproves of violence except in extreme circumstances. As for the last episode - oh no! Not another megalomaniac computer.'
Gordon Blows, reviewing the story in the Doctor Who Appreciation Society Yearbook 1977/78, also disliked the ending: 'Unfortunately, what started out to be an inventive and original story for Doctor Who disintegrated into a very over-used idea with the introduction of the Oracle. As the Doctor himself put it, "simply... another machine with megalomania!". The story became very close to... The Face of Evil, with the slaves taking the place of Leela's Sevateem and the robots the place of the acolytes.'
Like the same writers' earlier story The Invisible Enemy, Underworld relies to an unusually great degree on visual effects. The model work on this occasion is arguably some of the finest ever seen in the series, the best shot of all being the one where the R1C crashes through the soft surface of the newly-formed planet around the P7E. The realisation of the robotic Seers, on the other hand, is less impressive. 'It's never really explained who or what the Seers are,' noted Keith Miller in Doctor Who Digest Number 8, dated April 1978, 'but toward the end of [Part Three] they reveal themselves as they [lift] off their [masks] and we see two of the most hilarious aliens ever seen on TV. Two jumping beans with eyes!'
Undoubtedly the most contentious aspect of the production, however, is its very extensive use of CSO, by way of which all the scenes set in the caves of the planet were achieved. This has come in for some scathing criticism from reviewers, but is actually quite brilliantly done. Admittedly the viewer is never for one moment fooled into believing that the characters are walking through a real environment, but there is remarkably little of the peripheral fringing or image loss often associated with this effect (apparently it looks even better if watched in black and white) and in a strange sort of way it actually suits the slightly unreal quality of the Oracle's domain. In any event, given how difficult and time-consuming CSO effects can be to get right, one can only marvel at the technical prowess and commitment of all those involved in achieving these scenes.
There is far more to admire in Underworld than its reputation would suggest, and overall it stands up well as a good example of the Doctor Who of this period.