The experience will vary depending on the exact dramatization you read, but in general, a dramatization will be shorter and will eliminate many of the details in the interest of condensing the story for the sake of time. While you may see Scrooge reacting to the various ghosts who enter his room, you won't gain access to some of his deeper reflections. You'll miss the details of the original setting like this one described in the section when the Ghost of Christmas Present appears:

It was his own room. There was no doubt about that. But it had undergone a surprising transformation. The walls and ceiling were so hung with living green, that it looked a perfect grove; from every part of which, bright gleaming berries glistened. The crisp leaves of holly, mistletoe, and ivy reflected back the light, as if so many little mirrors had been scattered there...Heaped up on the floor, to form a kind of throne, were turkeys, geese, game, poultry, brawn, great joints of meat, sucking-pigs, long wreaths of sausages, mince-pies, plum-puddings, barrels of oysters, red-hot chestnuts, cherry-cheeked apples, juicy oranges, luscious pears, immense twelfth-cakes, and seething bowls of punch, that made the chamber dim with their delicious steam. In easy state upon this couch, there sat a jolly Giant, glorious to see; who bore a glowing torch, in shape not unlike Plenty’s horn, and held it up, high up, to shed its light on Scrooge, as he came peeping round the door.

The descriptive details of the story which give it so much depth are missing from dramatizations. While you might see some of these types of descriptors in stage directions or in staging arrangements, you can't possibly take in all the visual cues at once, even in a well-written dramatization, as is provided in the original text.

In a dramatization, you also miss some moments of Scrooge's transformation that are more evident in the original text, such as his feelings after inquiring about whether Tiny Tim will survive. When the Ghost of Christmas Present tells him that the child will die if the future remains unchanged, the original text says that Scrooge "was overcome with penitence and grief." A dramatization could convey that Scrooge is saddened, but to be overcome with grief is a much more compelling emotion and evidence of character change.

The sense of anticipatory dread which the final spirit brings is also lost in a dramatization. Consider Scrooge's initial meeting with this spirit:

The Phantom slowly, gravely, silently approached. When it came near him, Scrooge bent down upon his knee; for in the very air through which this Spirit moved it seemed to scatter gloom and mystery.

The original text effectively builds a tone that is crucial to understanding Scrooge's willingness to obey its commands. The Ghost of Christmas Yet to Come brings with it the power to make Scrooge feel his own impending doom, and some of this is lost in a dramatization.

Because of the speed at which dramatizations must cover the text, much of the depth, detail, and power of character analysis is lost at the expense of a faster retelling of the story. You will be able to recognize the basic plot structure and the main characters, but the original text is far superior in language and literary merit.