That is a tough question, because Oscar Wilde wrote a great story. It's hilarious because of the way that he wrote it. At first the reader believes that a standard, creepy ghost story is going to be told, but that notion is flipped on its head when the Otises refuse to be scared by the ghost and even frustrate the ghost with the help that they offer. The story is made even funnier by the fact that it is told from the ghost's perspective. This allows the reader into the thoughts of the ghost and really feel his frustrations.
If I had to pick something to change about the story, I might want to see what the story would be like if it were told from Virginia's perspective. The reader is told that she is different from the rest of the family and a bit different. This makes her separate from her family and separate from the ghost. This would make her a natural outside, objective viewer and story teller. I think the story would lose a lot of its humor if the narrator were Virginia. Her objectivity would likely fail to convey the thoughts and frustrations of the ghost appropriately. Still, it would make an interesting change to the story.