Readers have always loved Don Quixote. Critics, however, have offered mixed assessments of the novel. For example, Lord Byron asserted that Cervantes was responsible for finally extinguishing the flame of chivalry in Europe. This charge was repeated by the English author Ford Madox Ford. Other negative reviewers, like Miguel de Unamuno and Giovanni Papini, consider Don Quixote a brilliant novel but deem its author a disorganized hack.

Yet, these authors are in the minority. Most critics appreciate the achievement of the novel and the author. Highest praise for the author came from Victor Hugo: "Cervantes sees the inner man."

Don Quixote's popularity spread throughout Europe soon after the first English translation of the first part of the novel appeared in 1612. By the eighteenth century, Cervantes was a literary icon. In his biography of the author, Tobias Smollet recalled that dignitaries visiting Spain were appalled by the idea that Cervantes was not financially supported for his contribution to Spanish literature. Summarily, said Smollett, "Cervantes, whether considered as a writer or a man, will be found worthy of universal approbation and esteem."

William Hazlitt, in his "Standard Novels and Romances," examined a very popular subject of Cervantes criticism—the delightful characters. "The characters in Don Quixote are strictly individuals; that is, they do not belong to, but form a class of themselves." Hazlitt applauded the linguistic play of the author and the insights into human nature. Furthermore, Cervantes "furnished to the whole of civilized Europe" a great "number of allusions" useful for conversation and for sermonizing. Hazlitt ranked Cervantes with Le Sage as one of the great writers of the ages and ahead of Fielding, Richardson, Smollett and Sterne on the local English stage.

Unlike Lord Byron, many commentators were thankful that Cervantes had, as Heinrech Heine contended, "uprooted the tales of chivalry." Heine asserted that after Don Quixote the "taste for such books died." Indeed, "Cervantes founded the modern novel by introducing into the knightly romance the faithful delineation of the lower classes—by giving the life of the people a place in it."

Carlos Fuentes maintained that if Don Quixote is the first modern novel then his "debt to tradition is enormous." Another critic, the noted author Vladimir Nabokov, agreed:

I wish to stress the fact that in romances of chivalry all was not Ladies and Roses and Blazons, but that scenes occurred in which shameful and grotesque things happened to those knights and they underwent the same humiliations and enchantments as Don Quixote did—and that, in a word, Don Quixote cannot be considered a distortion of those romances but rather a logical continuation, with the elements of madness and shame and mystification increased.

Cervantes is often compared with his English contemporary, William Shakespeare. For example, Wyndham Lewis compared the character of Don Quixote to Falstaff. Ivan Turgeniev, in "Hamlet and Don Quixote" made a more immediate comparison: While Hamlet represents the Northern European archetype, Don Quixote represents the Southern European man. This man is characterized by his affinity for a romantic view of the Middle Ages. Perhaps Don Quixote is more limited than Hamlet but he "reflects all that is human … [he is a] deep river quietly flowing [with which] the reader, slowly carried by its transparent waves, looks with joy at that really epic tranquility."

Believing that Cervantes was sent by God solely to give us Don Quixote, Miguel de Unamuno asserted, "Cervantes never existed but Don Quixote did." As if that were not clear enough, Unamuno categorically declared, "I have no doubt in my mind but that Cervantes is a typical example of a writer enormously inferior to his work, to his Don Quixote." However the novel came into being, Unamuno admitted that Don Quixote is as much an artifact for meditation as anything Homeric or, for the English, anything Shakespearean.

The master of magic realism, Jorge Luis Borges, considered Don Quixote his muse. His remarks, characteristically, analyze the theme of reality: "Every novel is an ideal depiction of reality." He asked the troublesome question, "Why does it make us uneasy to know that the map is within the map ….. that Don Quixote is a reader of the Quixote, and Hamlet is a spectator of Hamlet?” The answer is such: "Those inversions suggest that if the characters in a story can be readers or spectators, then we, their readers or spectators, can be fictitious."

The theme of madness is a recurring subject of Cervantes commentary. Recent criticism of the psychological vein has been insightful. Caroll B. Johnson speculated on the relationship between Don Quixote and his loyal sidekick, Sancho. He perceived homoerotic elements in their friendship; moreover, he considered the relationship a life-affirming example of how men can be friends with men.

Carroll summarized his view of Quixote: "Don Quixote's madness propels him backward into life. It enables him to have a life, to engage in purposeful and meaningful activity, and to enjoy a fulfilling, evolving relationship with another human being. That is, in the psychological as well as the existential sense already observed by Unamuno, our fiftyish hidalgo's only meaningful life is his life as a madman Don Quixote ….. [therefore, readers] are saddened by his recuperation of sanity and his swift death."