I hate how in their adaptation they did mass character assassination of all the Whos down in Whoville, where they as a whole do not really understand the true meaning of Christmas and the Grinch has to learn it (although how he "learns" it is suspect) and how the Whos suddenly "get" it. In the original, it's the Grinch seeing the Whos still gathering around and joyfully singing despite having lost everything that taught the lesson that Christmas isn't about gifts and presents and trees and decorations. In the Jim Carrey version, the Whos certainly haven't even learned that lesson themselves; only Cindy Lou wonders if there's more, but I don't think it's very definitive how the lesson gets learned and internalized.
However, there are some fine Jim Carrey moments with many memorable quotes and actions that make the movie worth watching even if they did the story all wrong.