In a contemporary review for the
Monthly Film Bulletin, Michael Grossbard described ''Satan's Slave'' as "basically an archaic
second feature" and "the sort of subject likely to turn up on Sunday afternoon children's television, with its kids-in-trouble/blame-the-older-generation theme." He considered the plot "well constructed and written" and the performances "never below standard, though it would be nice to see Michael Gough in more demanding parts." The film was negatively received by the
Coventry Evening Telegraph and the
Aberdeen Press and Journal. David Parkinson of
Radio Times gives three stars out of five, concluding that Warren "ultimately overindulges in horror clichés and garish set pieces".
TV Guide magazine describes it as a "vile shocker [...] full of unappetising gore effects", By contrast, Martin Unsworth of
Starburst magazine names it "one of the big underrated movies of the '70s" and a "vital entry to the British horror pantheon". Gary Raymond and Gray Taylor of
Wales Arts Review rank the film 21st in their list of the "50 greatest" lesser-known horror films. Reviewing the film for
DVD Talk in 2004, Bill Gibron described Gough's character as a "grey Sunday drag of a villain" and ''Satan's Slave'' in general as a "near-immobile mess", adding: "With an ending that repeats, laps and then doubles back on itself, and an overall atmosphere of dismal dissatisfaction, the only suggestive thing about this movie is its titillating title." In another review published in 2012, he gave three out of five stars, judging the script "silly" and the atmosphere "often wasted" but praising the performances of Gough and Glendenning. He wrote: "[...] if you can get past the endless conversations, [the] lack of real suspense, the flawed feeling of familiarity and the dearth of any or all plot twists toward the end [...] then by all means saddle up and strap in". Ian Jane, also of DVD Talk, writes that while the film has "some rather obvious pacing problems" and less suspense than a
Hammer horror, it still "has its moments". Dennis Schwartz of the
Online Film Critics Society rates the film "C+", believing it to be "directed with high production values but with little else that rocks". He considers the script "weak" and the dialogue "abominable", the overall film "clichéd" and the final plot twist a non-surprise as it is "given away in the opening act". Despite calling the car crash "amusingly badly staged", commentator Ian Fryer believes that film's "attractive" locations and "excellent" performances make it "[look] like a much more expensive production than was actually the case." He adds that the level of violence "made the products of the declining Hammer and
Amicus studios look like very mild fare indeed." Steve Green of
Flesh and Blood magazine writes that despite its "formulaic construction" the film is Warren's "most effective horror entry" and "head and shoulders above the
stalk/
slash tedium which would dominate the American industry within five years."
Kim Newman, who regards ''Satan's Slave'' as the "most conventional" of Warren's films, compliments its "very low-budget imagination" as well as Gough's "committed" performance. Rating the soundtrack nine out of ten, Unsworth describes Scott's score as "a stunning piece of work, melding some erratic styles perfectly and creating a genuine atmosphere of dread with each listen". ==References==