There is a layer of subtle terror in Zemeckis' depiction of the Ghost of Christmas Future as an incorporeal shadow. With this spirit Scrooge has no companion to serve as a guide or confidant to share his thoughts. At the beginning when Scrooge talked to the charity men, he said he wished to be left alone, and now he truly is alone.
Marley being stuck as a spirit gains a new explanation in this version. At the funeral scene, the first thing Scrooge does is steal the coins from Jacob Marley's eyes. The custom of putting coins on the eyes of the dead stemmed from a superstition that unless blinded, the dead could open their eyes and seek out others to join them in death, but an even older version of the custom dates back to Greek Mythology: When your soul entered the afterlife, you would be ferried across the River Styx by Charon, the ferryman, who required payment. Two coins were left with the bodies so that they could be used to pay Charon. Scrooge stole Marley's coins, thus Marley can't pay his way, so he is Barred from the Afterlife.
We see Ignorance and Want grown to adulthood. Ignorance seems to spend his life in and out of jail, while Want, a girl, possibly goes down another path of ill-repute. The Brilliance comes when Scrooge is dealing with the Ghost of Christmas Yet To Come, and sees the two people picking through his belongings once he's dead. They look a lot like Ignorance and Want.
Want also gets put in a straitjacket, suggesting a mental asylum. Some venereal diseases—syphilis, particularly—have that effect on the brain and, by extension, the mind.
Scrooge's heartfelt and effusive thanks to the Charity Solicitor was partially to Jacob Marley.
Why was Jim Carrey credited for the role of Christmas Yet to Come who never actually spoke at any point in the movie? We are not supposed to know what the future will tell us so the most we can only do is guess or interpret before or once it happens. And that is what Scrooge did. He interpreted the Ghost's thoughts projected into his mind for us. Without him, we have to guess or interpret what the Ghost is trying to show, tell or do to Scrooge.
Want gets put in a straightjacket. Now consider how awful asylums could be in those days. Even if the doctors wanted to help, they didn't necessarily know how, and things there too often went very badly.