Nearly worthless. It's not bad as such, but it's boring.
The story involves a woman who invites men for sex and then kills them. It's more thriller than horror, to be honest. The hero's a police detective and we follow him as he goes about his investigations, who's several steps behind the audience for almost the whole episode. Now in principle this is fine. It's also clearly deliberate, since they make a point of showing us the killer's face. Hitchcock did it a lot, but he did so for the purposes of suspense rather than to spend half the episode having the police following up leads that the audience know are a waste of time.
The pre-credits sequence shows us that the killer is a sexy woman. She even gets naked, just to kill any ambiguity. Nevertheless the police will later be wondering if it's a man, then go chasing the world's worst female impersonator. (We're meant to think he's good, but really. You'd pay him to shut up and get off the stage.)
The real problem though is that I didn't care about any of the characters. A whodunnit can succeed even with wooden characterisation, or alternatively a thriller can be terrifying if the audience are emotionally involved. Unfortunately this episode has neither. The plot leaves us no questions to think about, while the characters are all people you'd happily see dead. All that's left is a charmless police procedural with enough nudity to activate the dreaded "nudity in Hammer House of Horror" rule and ensure that the episode is a waste of time. (I offer no explanation of this phenomenon. I merely report on it. Believe it or not, the sight of a bare bottom in the pre-credits sequence nearly made me swear, on the assumption that the episode was now doomed.) Admittedly we never see tits, all the nudity being from behind, but there's still enough here to suggest to me that the director enjoys the sight of the female form.
Going through the cast, we have:
(a) the killer, who goes around killing. The actress also has so little screen presence that I wasn't sure if she was the same person we'd been watching earlier, despite whacking great close-ups of her face on both occasions. She's a shapely null.
(b) the detective, who's businesslike to the point of being faintly unpleasant.
(c) the victims, who all deserve it.
The biggest name here is a disturbingly young Pierce Brosnan as "Last Victim". That was freaky. Don't expect to see too much of him, though. Obviously in 1980 he was still a nobody, getting his first ever screen credits and also playing "1st Irishman" in The Long Good Friday. Apart from him though there's Suzanne Danielle (famous back then for being sexy), Anthony Valentine (former child star and so the owner of an absurdly long screen career) and Sian Phillips (Livia in I, Claudius). My usual Doctor Who round-up yields:
1. Jeffrey Wickham -- The Reign of Terror (1964), Webster
2. Suzanne Danielle -- Destiny of the Daleks (1979), Agella
3. Barry Stanton -- The Twin Dilemma (1984), Noma
4. William Morgan Sheppard -- The Impossible Astronaut (2011), Old Canton Delaware
It tickles me to see The Reign of Terror and The Impossible Astronaut side-by-side like that.
In fairness, some people like this episode. It does what it says on the tin, so to speak. Police investigate sexy serial killer. You could probably sell a Hollywood remake. Personally though I found nothing whatsoever of interest in it, even though it's basically competent and doing nothing screamingly wrong. I think it's basically hitting the marks the writer and director had in mind.
Okay, maybe Pierce Brosnan doesn't deserve to die, but that's mostly because he doesn't get enough screen time for that. The final twist seemed pointless to me too. Avoid.