I agree, Eliza, that correct casting is vital. One example where this was well achieved was in David Lean's much admired 1940s Great Expectations -- in all but the two main parts, unfortunately: John Mills was too old, and Valerie Hobson not quite exquisite enough. But Bernard Miles's Joe, Freda Jackson's Mrs Joe, Ivor Barnard's Wemmick, Francis L Sullivan's Jaggers, Alec Guinness's Herbert, Martita Hunt's Miss Havisham. Jean Simmons's Young Estella, Finlay Currie's Magwitch -- all could have stepped right off Dickens's pen. Unfortunately, the thing was marred by the over-dramatic telescoping of Dickens's long-drawnout ending [Pip doesn't see Estella again for about 12 years, and then it is left ambiguous as to whether they get it together again -- and that was a rewritten ending, by popular demand, from the one in the original edition where they are parted for ever!]; and, above all, by the entire omission of the character of Dolge Orlick and his attempt to murder Pip, which left a great hole in the plot which the film never satisfactorily filled.

~M~