"As in its author's previous fictions, we are almost oppressed by the fulness of life which pervades the pages of this novel. Mr. Dickens has one of the most mysterious attributes of genius -- the power of creating characters which have, so to speak, an overplus of vitality, passing beyond the limits of the tale, and making itself felt like an actual, external fact. In the stories of inferior writers the characters seem to possess just sufficient personality and presence to carry on the purpose of the narrative; one never thinks of them as enjoying any existence at all outside the little tissue of events that has been woven for them. They are ghosts whom the author has evoked out of night and vacuity to perform certain definite offices within the charmed circle of the fiction to which they are attached; and when we step out of that circle at the conclusion of the ceremonies, they vanish again into nothingness, and we think no more of them. Such is not the case with the conceptions of larger geniuses. These do not seem to belong wholly to the one set of events with which they are associated, any more than the men and women we actually know present themselves to our thoughts as the puppets of a definite train of circumstances. The creations of authors such as Mr. Dickens have a life of their own. We perceive them to be full of potential capacities -- of undeveloped action. They have the substance and the freedom of actual existences; we think of what they would do under our conditions, they are possessed of a principle of growth."
London Review, October 28, 1865, quoted in Charles Dickens's Our Mutual Friend: A Publishing History