What not to miss at Williamsburg VA.....

It all depends on what you're looking for, as others have said, Busch Garden which is a theme Park, if you're into that, or if you're into the history, there is Colonial Williamsburg, Jamestown, a National Park which is the first "Permanent" English settlement, then there is Jamestown Settlement, which has three Ships you can visit, A Powhatan Indian village, and a Settlement Fort.
If you haven't had enough history by then, you can take the Colonial Parkway over to Yorktown for the Revolution History. Or head out Rt 5 for the Berkley, or Shirley Plantations.