Don Quixote is universally regarded as Cervantes' masterwork and one of the greatest novels of all time.
The novel is actually two separate books that cover the adventures of Don Quixote, also known as the knight or man of La Mancha, a hero who carries his enthusiasm and self-deception to unintentional and comic ends. On one level, Don Quixote works as a satire of the romances of chivalry which ruled the literary environment of Cervantes' time. However, the novel also allows Cervantes to illuminate various aspects of human nature by using the ridiculous example of the delusional Quixote.
Cervantes felt a passion for the vivid painting of character, as his successful works prove. Under the influence of this feeling, he drew the natural and striking portrait of his heroic Don Quixote, so truly noble-minded, and so enthusiastic an admirer of every thing good and great, yet having all those fine qualities, accidentally blended with a relative kind of madness; and he likewise portrayed with no less fidelity, the opposite character of Sancho Panza, a compound of grossness and simplicity, whose low selfishness leads him to place blind confidence in all the extravagant hopes and promises of his master. The subordinate characters of the novel exhibit equal truth.
Were it not for the happy art with which Cervantes has contrived to preserve an intermediate tone between pure poetry and prose, Don Quixote would not deserve to be cited as the first classic model of the modern romance or novel. It is, however, fully entitled to that distinction. Cervantes was the first writer who formed the genuine romance of modern times on the model of the original chivalrous romance, that equivocal creation of the genius and the barbarous taste of the Middle Ages. The result has proved that modern taste, however readily it may in other respects conform to the rules of the antique, nevertheless requires, in the narration of fictitious events, a certain union of poetry with prose, which was unknown to the Greeks and Romans in their best literary ages. It was only necessary to seize on the right tone, but that was a point of delicacy, which the inventors of romances of chivalry were not able to comprehend. Diego de Mendoza, in his Lazarillo de Tormes, departed too far from poetry. Cervantes, in his Don Quixote restored to the poetic art the place it was entitled to hold in this class of writing; and he must not be blamed if cultivated nations have subsequently mistaken the true spirit of this work, because their own novelists had led them to regard common prose as the style peculiarly suited to romance composition.
Don Quixote is, moreover, the undoubted prototype of the comic novel. The humorous situations are, it is true, almost all burlesque, which was certainly not necessary, but the satire is frequently so delicate, that it escapes rather than obtrudes on unpractised attention; as for example, in the whole picture of the administration of Sancho Panza in his imaginary island. The language, even in the description of the most burlesque situations, never degenerates into vulgarity; it is on the contrary, throughout the whole work, so noble, correct and highly polished, that it would not disgrace even an ancient classic of the first rank. This explanation of a part of the merits of a work, which has been so often wrongly judged, may perhaps seem belong rather to the eulogist than the calm and impartial historian. Let those who may be inclined to form this opinion study Don Quixote in the original language, and study it rightly, for it is not a book to be judged by a superficial perusal. But care must be taken lest the intervention of many subordinate traits, which were intended to have only a transient notional interest, should produce an error in the estimate of the whole. By the 20th century the French writer Dominique Aubier discovers that Don Quixote was the first true modern novel, a systemical and structural masterpiece in fact coded in kabalistic keys.