The episode features some excellent visual effects (Gwent itself is marvellous), the acting is good and there are some poignant moments.
(Richard Houldsworth, TV Zone, 1992)
Most 60s and 70s SF TV series also did a 'super computer episode sooner or later and once again 1999's is cut from superior cloth. Leo McKern is superb in a dual role and Gwent's final moments are very touching. A+
(Chris Bentley, SFX 20, 1996)
Despite the solid concept and interesting central character, The Infernal Machine is only a slightly better than average episode. David Tomblin fails to keep this story moving forward satisfactorily. The well staged, beautifully executed Eagle/tank assault on Gwent, along with Leo McKern's excellent performance, enliven the story but there is an essential element of urgency missing from the script.
(John Kenneth Muir, Exploring Space: 1999, p73-74)
McKern is typically good in this okay tale of a lonely alien machine. **- (average)
(James O'Neill, Sci-Fi On Tape, p271, 1997)
The script is rich in humanity and a deep depth of characterisation. The pace and plotting are ideally matched with the demanding emotional qualities of the show. The Infernal Machine is suspenseful to the end, visually beautiful and is undoubtedly the most touching and gently endearing segment of the series. 9.5/10
(Bob Wood, The Future Is Fantastic, 2001)
This is a good and somewhat unusual take on the "living ship" story. 3/5
(Alasdair Stuart, SciFiNow #10, 2007)