'Warriors of the Deep' is not an especially popular story, and this is often attributed to a decent script let down by poor production values. But personally, I'm not even that enamoured of the script, and whilst I do quite enjoy 'Warriors of the Deep', it is deeply flawed in many aspects.
Firstly, I'll discuss the Silurians and the Sea Devils. The nature of the Silurians is such that any story in which they feature potentially offers a moral dilemma for the Doctor; the Silurians, after all, have a legitimate claim to Earth, and they want it back. Humanity also has a legitimate claim to Earth and they don't want to give it back. Whilst some humans and some Silurians might be willing to share the planet, others would not; given the racial intolerance between different races of humans, the possibility that the world's human population would accept another species is sadly unlikely. The consequence of which is inevitably bloodshed; this was the case in 'Doctor Who and the Silurians' and 'The Sea Devils', and it's the case here. The result of which means that the Doctor can almost certainly never achieve the peaceful solution he'd prefer, meaning that he inevitably has to take sides with one of two species neither of which he is a member. Since the Silurians (or in their debut, some Silurians) keep attempting genocide, he usually of course sides with the humans. This moral quandary is central to the story potential of the Silurians, but the only reason I know that is because I've seen 'Doctor Who and the Silurians' and 'The Sea Devils'; the much-vaunted script of 'Warriors of the Deep' does bugger all with the concept.
This is my main criticism of 'Warriors of the Deep'; there is no dissenting voice amongst the Silurians or Sea Devils, they are all committed to genocide. A new viewer has no real reason to sympathize with their plight, since Byrne's only acknowledgement of it is in a mere handful of lines. The Doctor talks of the honourable nature of the two reptile races, but we see little of it on screen. Ichtar's talk of offering the hand of friendship twice before is not elaborated on and therefore has little impact and his actions unfortunately speak far louder than words. By the end, with everyone dead save for the Doctor and his companions, the Doctor's quiet assertion that "there should have been another way" is presumably an attempt to inspire regret at the lack of a peaceful solution, but the hostility of the Silurians and Sea Devils throughout has been such that it might more reasonably provoke the response "Yes, you should have bloody well flooded the base with hexachromite gas two episodes earlier Doctor!". Incidentally, whilst this is irrelevant to the success or lack therefore of 'Warriors of the Deep', I also find it quite amusing that the continuity on display is clearly aimed at long term fans, but only long term fans would realize that the continuity is crap; allegedly, Ichtar is meant to be the Silurian Scientist from 'Doctor Who and the Silurians', but this doesn't really work and neither does his description of past encounters with humanity. The most sensible assumption for anyone who feels worried by this is that Ichtar is describing an untelevised adventure, and indeed Gary Russell's 'The Scales of Injustice' plugs this gap nicely! But anyway, back to the matter in hand
Criticisms of the script bring me to hexachromite, an obvious plot contrivance introduced far too early on and almost embarrassingly convenient (Lethal to all reptile and marine life you say? Lucky you had some lying around then ). And whilst I'm on the subject, the equally convenient realization that there are ventilation shafts big enough to crawl through running throughout the base seems equally contrived; it's a cliché common to other Doctor Who stories, including the superb 'The Ark in Space', but with such a weak script as the one here, it strikes me as more of a cheap plot device than usual.
The remainder of the plot concerns the function of the Sea Base and its role in Earth's political situation in the year 2084, and it is a bit better handled than the Silurian plot. The idea of two opposing power blocs was very topical at the time, but the handling of it here renders it slightly moronic; the decision to keep these two power blocs unspecified results in some clumsy dialogue as Nilsen claims that he works for the power bloc opposed to the Sea Base as though he's forgotten what it's called. Still, the world poised on the brink of nuclear Armageddon makes for a suitably morose backdrop to the story and this comes over reasonably well. It is quite well known that Byrne wanted gloomy, cramped sets to evoke the feeling of a submarine and to convey the fact the Sea Base and its personnel are operating under desperate conditions, but instead he gets brightly lit gleaming sets. Despite this, the air of tension on board the Sea Base is well handled due to the characterisation, especially of Maddox, a student forced prematurely into the role of Synch Op for which is he is patently unsuited. Martin Neil's twitchy, sweaty performance is superb, effectively creating the impression of a man in a vital role who is unable to cope with his newfound responsibilities. The desperate situation is made plain throughout, the need for radio silence to be maintained meaning the Sea Base personnel are forced to fight an enemy that totally outclasses them, and also forcing Vorshak to release Maddox's conditioning disc.
But whilst the script does reasonably well at depicting the difficult conditions under which the Sea Base has to operate, certain members of the guest cast do not help. Ian McCulloch's Nilsen is quite effective, since he seems to be genuinely driven by duty and ruthless rather than sadistic. His co-conspirator unfortunately is less impressive; Ingrid Pitt hams it up in the role of Solow, culminating in a deeply embarrassing karate attack on the Myrka. Nigel Humphreys' down-to-earth Bulic is rather good and as the pragmatic Vorshak, Tom Adams brings a certain authority to the role, but as the story progresses it becomes clear that his performance is a bit too laid back. By the time Vorshak tells Ichtar that he won't be responsible for the destruction of his own kind, he sounds like he's complaining about the weather.
The regulars are reasonably well used, save for Tegan who does little except follow the Doctor around so that he can explain things to her. The Doctor himself comes over very well, Davison putting in a frantic performance as the Doctor strives in vain for a peaceful solution. His near drowning at the end of Episode One is well realised although his surrendering of his gun in order to gain Vorshak's trust is hardly original, the same trick having been used several times before in the series. Turlough is very well used; his innate cowardice is explained here as pragmatism, as he twice abandons the Doctor because he genuinely believes that his friend is dead and he doesn't fancy throwing his own life away for the sake of a futile gesture. When he believes that he can help however, he does; when he pulls a gun on Nilsen to force him to open the airlock door and thus save the Doctor and Tegan he puts his own life at risk because he knows it might work.
And what of the often-criticized production? The extensive sets are actually very good they just aren't what Byrne wanted. The costumes of the Sea Base personnel have aged very badly, and the big hair and eye shadow firmly place this story in the midst of the nineteen eighties. The Silurian and Sea Devil costumes are rather poor; the redesigned Silurians look the worst, appearing cross-eyed; the controversial decision to have their third eyes flash when they speak merely highlights the fact that the actors are unable to make it clear that they are speaking in the inflexible costumes, whereas this wasn't a problem in 'Doctor Who and the Silurians'. Their new voices are also poor, making them sound like Cybermen (especially since Ichtar keeps saying "Excellent!"). The Samurai Sea Devils are truer to their originals as are their voices, but the costumes fit poorly and the actors waddle about in a cumbersome fashion, which makes them look more comedic than they did in 'The Sea Devils'. The much-derided Myrka does indeed look quite bad, although no worse than many other large monsters in Doctor Who. In fact the overly flexible airlock door is far more irritating; surely the designer could have used something that wobbled less? On the other hand the model work is excellent, especially that used for the Sea Base. Jonathon Gibbs' incidental score is also very good, and helps to salvage the atmosphere somewhat, but it isn't enough. 'Warriors of the Deep' is strangely enjoyable, but it is also deeply flawed and overall proves to be a weak start to Season Twenty-One.