In the same month as the second edition was published, Samuel Taylor Coleridge wrote a piece in The Critical Review, an important literary magazine of the day, in which he both praises and criticizes the novel harshly. He acknowledges that it is “the offspring of no common genius,” that the “underplot... is skilfully and closely connected with the main story, and is subservient to its development,” that the story Lewis weaves in about the bleeding nun is “truly terrific” and that he cannot recall a “bolder or more happy conception than that of the burning cross on the forehead of the wandering Jew.” Coleridge gives his highest praise to the character of Matilda, whom he believes is “the author’s master-piece. It is, indeed, exquisitely imagined, and as exquisitely supported. The whole work is distinguished by the variety and impressiveness of its incidents; and the author everywhere discovers an imagination rich, powerful, and fervid. Such are the excellencies” (7). Coleridge continues by saying that “the errors and defects are more numerous, and (we are sorry to add) of greater importance.” Because “the order of nature may be changed whenever the author's purposes demand it” there are no surprises in the work. Moral truth cannot be gleaned because Ambrosio was destroyed by spiritual beings, and no earthly being can sufficiently oppose the “power and cunning of supernatural beings.” Scenes of grotesquery and horror abound, which are a proof of “a low and vulgar taste.” The character of Ambrosio is “impossible... contrary to nature.” Coleridge argues that the most “grievous fault... for which no literary excellence can atone” is that “our author has contrived to make [tales of enchantments and witchcraft] ‘ ‘pernicious’ ‘, by blending, with an irreverent negligence, all that is most awfully true in religion with all that is most ridiculously absurd in superstition,” commenting with the immortal line that “the Monk is a romance, which if a parent saw in the hands of a son or daughter, he might reasonably turn pale.” Coleridge finishes the piece by explaining that he was “induced to pay particular attention to this work, from the unusual success which it has experienced” and that “the author is a man of rank and fortune. Yes! the author of the Monk signs himself a LEGISLATOR! We stare and tremble.”
Thomas James Mathias followed Coleridge’s lead in The Pursuits of Literature, a poem in the 18th-Century satiric tradition, but takes a step farther than Coleridge by claiming that a specific passage made the novel indictable under law. The passage, found in Chapter Seven Volume II, discusses an interpretation of the Bible as too lewd for youth to read.
These two major pieces lead the way for a multitude of other attacks on the novel, from such sources as the Monthly Review, the Monthly Magazine, and the Scots Magazine; the last of these attacked the novel six years after its publication. It was a general trend amongst those who criticized, however, to offer praise of some aspect of the novel. “It looked,” writes Parreaux, “as if every reviewer or critic of the book, no matter how hostile he was, felt compelled to at least pay lip-service to Lewis’s genius.”
The criticism of his novel, extending even into criticism of his person, never truly left Lewis, and an attack on his character was published by the Courier posthumously, calling itself a “just estimate of his character.” As recorded by MacDonald: “He had devoted the first fruits of his mind to the propagation of evil, and the whole long harvest was burnt up ... There is a moral in the life of this man ... He was a reckless defiler of the public mind; a profligate, he cared not how many were to be undone when he drew back the curtain of his profligacy; he had infected his reason with the insolent belief that the power to corrupt made the right, and that conscience might be laughed, so long as he could evade law. The Monk was an eloquent evil; but the man who compounded it knew in his soul that he was compounding poison for the multitude, and in that knowledge he sent it into the world.” 
There were those who defended The Monk as well. Joseph Bell, publisher of the novel, spent half of his essay Impartial Structures on the Poem Called “The Pursuits of Literature” and Particularly a Vindication of the Romance of “The Monk” defending Lewis; Thomas Dutton, in his Literary Census: A Satirical Poem, retaliated against Mathias and praised Lewis; Henry Francis Robert Soame compared Lewis to Dante in his The Epistle in Rhyme to M. G. Lewis, Esq. M. P.
“Assurances that The Monk was not as dangerous as its enemies maintained failed to dampen its success with the reading public,” writes Peck. “They had been told that the book was horrible, blasphemous, and lewd, and they rushed to put their morality to the test.” Indeed, the novel’s popularity continued to rise and by 1800 there were five London and two Dublin editions.