The website's critical consensus reads, "Tahar Rahim's unnerving performance brings reptilian menace to The Serpent, but this uneven slice of true crime is too byzantine in structure and too pat about its central villain's motivations to really get under the skin.

Rebecca Nicholson, writing in The Guardian, gave the first episode 3/5 stars, finding the time-hopping plotting unnecessary and confusing, and wondering whether the programme had much to say, while admiring the atmosphere and the 'routinely outstanding cast'.

[18] For Euan Ferguson writing in The Observer, who admired Rahim and Coleman's acting, The Serpent was a 'skilful retelling' of the Sobhraj story and one that both pays homage to his victims, while revealing the cultural shortcomings of the flower children.

[19] However, Rahim's absence of charisma makes it hard to understand how Sobhraj gained a hold over people for Flora Carr, writing in The Radio Times, who gives the show 3/5 stars.

[20] Giving the programme 3/5 stars, Ed Cumming in The Independent found the pace slow and Rahim's acting staying mostly on the right side of the fine line between inscrutable and dull.

[21] James Delingpole in The Spectator called it "the best BBC drama series in ages", admiring the period detail, superb casting and absence of "unnecessary politics" as well as noting that it might be especially painful for people who could have found themselves in similar scenarios to those that Charles Sobhraj exploited.

[22] By mid-point The Serpent gathers "considerable momentum" according to Trevor Johnson in Sight and Sound reviewing the first four episodes, who goes on to write that the series features an "alluring anti-hero" and excellent score, but is let down by the shallow characterisation of its Thai characters.

[23] Rahul Desai of Film Companion called The Serpent “a refreshing restoration of balance" adding that it "reduces Charles Sobhraj from an image to an individual, a portrait to a person – and most importantly, from a human to a reptile.

[25] The journalist Andrew Anthony, who interviewed Sobhraj twice, said that while the series captured his "enigmatic detachment and quiet menace", it misses his more troubling qualities of wit, charm and "a kind of playful sense of self-mythologising".