Lots of fun! It's great to be able to do everything at exactly your own pace. No waiting for somebody to finish using the toilet or buy a churro when you just finished six Dole Whips. If you don't mind being alone you should have a great time.
I have a funny plan to go to Florida a couple of days before my expected arrival date (to start my internship) just so I can have some fun by myself before its time for me to start work (and to perhaps get a better understand of my surroundings since I will be there for five months. I was even thinking about spending a couple of nights in a Disney hotel and stuff. I dont think my parents will go for it. It would be cool though!
Back in the days when I vacationed rather than worked at Disney World, the best trip I ever had was when I went alone.
I did what I wanted, when I wanted. No waiting for anyone, no compromises, nothing.
If YOU want to go to Disney World, and can't find no one else that can/wants to go with you, there's no reason wy you can't do it alone. Same for any vacation destination.