Great Expectations is considered by many to be Dickens' masterpiece.  Like its preceding novel, A Tale of Two Cities, it is among the shorter full novels of Dickens (only "Hard Times" is shorter than these two) at about 600 pages each.  Dickens tried to study the effect of inheritance on a human being.  Philip Pirrup (Pip) is an orphan with only one older sister, and lives with his sister, her husband the village blacksmith and Biddy.  Despite his sister's harshness, Pip has a decent life.

One day, when visiting the graves of his parents, Pip is surprised by an escaped convict.  The convict threatens Pip, who returns with food and supplies for him.  Pip doesn't say anything to the anyone about the convict, but just helps him.  However, the convict is caught, but he realizes Pip had been true to him.  He thanks the boy before being taken away.

Some years later Pip is invited to the home of an eccentric wealthy woman named Mrs. Haversham.  He is taken there and meets her lawyer, Mr. Jaggers, a young boy (who we later learn is one Herbert Pocket) and a proud, beautiful young girl named Estella.  Pip is to come several times a week to play cards with Estella (who keeps denigrating him), to the amusement of Mrs. Haversham.  The old lady was the victim of betrayal when getting married, and hates the world as a result.  When Estella complains about Pip being so common, Mrs. Haversham whispers to her, "You can break his heart!"

One day, Jaggers tells Pip and Joe that Pip has obtained a patron—he is to be brought up to be a gentleman by an unknown benefactor.  Jaggers says that he has "great expectations" for Pip's future as a result.

That's the background.  Mills slowly turns from incredulous type into a terrible snob—even making poor Joe and Biddy feel out of place in his presence.  He pursues Estella who, despite his rise, still considers him a poor boy.  He also considers that Mrs. Haversham is his benefactor, but he isn't sure.   Then he is surprised to meet the real benefactor, Abel Magwich, and discovers that great wealth does not come from "gentleman" all the time.

The film omits much of the original story, such as subplot involving an attack on Mrs. Joe by an poor farm hand named Orlick, and a moment of melodrama aimed at Pip by Orlick later on.  There is not enough about Pip's rival for Estella, a super snob named Bentley Drummle.  The problem of transporting of criminals to Australia and the rules regarding their returning is not really discussed in the film.  Instead it is the effect of wealth on people that is the center of the film version, and the film is stronger as a result.

Mills had one of his best early roles as the hero who discovers that there are fine human beings who don't need money.  Simmons and Hobson are properly selfish as Estella.  Guinness is pleasant as Pip's closest friend (but the role is not as rich as his Fagin in Oliver Twist).  As was pointed out, Sullivan gives a sturdy performance as a man in a corrupt profession in a corrupt world, who tries to help people.