Satan’s ambition, unflinching pursuit of power, and equally unflinching endurance of pain made him for the critic William Hazlitt “the most heroic subject that ever was chosen for a poem.” Hazlitt discussed Paradise Lost at length in the second of the public lectures on the history of English poetry that he delivered in 1818.
The Achilles of Homer is not more distinct; the Titans were not more vast; Prometheus chained to his rock was not a more terrific example of suffering and of crime
>> note 1 . Wherever the figure of Satan is introduced, whether he walks or flies, 'rising aloft incumbent on the dusky air,'
>> note 2 it is illustrated with the most striking and appropriate images: so that we see it always before us, gigantic, irregular, portentous, uneasy, and disturbed—but dazzling in its faded splendour, the clouded ruins of a god. The deformity of Satan is only in the depravity of his will; he has no bodily deformity to excite our loathing or disgust. The horns and tail are not there, poor emblems of the unbending, unconquered spirit, of the writhing agonies within. Milton was too magnanimous and open an antagonist to support his argument by the bye-tricks of a hump and cloven foot; to bring into the fair field of controversy the good old catholic prejudices of which Tasso and Dante
>> note 3 have availed themselves, and which the mystic German critics would restore.
>> note 4 He relied on the justice of his cause, and did not scruple to give the devil his due. Some persons may think that he has carried his liberality too far, and injured the cause he professed to espouse by making him the chief person in his poem. Considering the nature of his subject, he would be equally in danger of running into this fault, from his faith in religion and his love of rebellion; and perhaps each of these motives had its full share in determining the choice of his subject.
—From Lectures on the English Poets (1818)