I just came across this lovely passage from G. K. Chesterton's introduction to it:
We go for a particular novel to Dickens as we go for a particular inn. We go to the sign of the Pickwick Papers. We go to the sign of the Rudge and Raven. We go to the sign of the Old Curiosities. We go to the sign of the Two Cities. We go to each or all of them according to what kind of hospitality and what kind of happiness we require.
Rather unfortunately, Chesterton goes on to argue that Martin Chuzzlewit is the exception to the rule, thanks to its "melancholy" feel. Still, the imagery is brilliant and, I think, profoundly true.
And Chesterton does go on to say, "He poured into this book genius that might make the mountains laugh, invention that juggled with the stars." So there's that!