The uniqueness of Drayton Hall lies in the fact that the house itself is about 275 years old and -- in all that time -- it's never been significantly altered or modernized. As cliched as it may sound, it really is like going back into time. The house tour (about 45 minutes) is very informative and stresses the mission of preservation of the structure rather than restoration. The house is not furnished, resulting in a real "bare bones" kind of feel inside. The formal balanced Georgian architecture is really beautiful and inside there are lovely moldings, columns, capitals, etc. Without the distractions of interior furnishings, you can really appreciate the fine details.
The property is lovely with a wonderful Ashley River view, but don't come here expecting formal gardens because there are none. There is, however, a not-too-long marsh walk with a brochure that explains points-of-interest along the way. There is also an African-American cemetery on the property. I've now visited all three historic plantations on the Ashley River and they are each worth seeing for their own unique flavor. There are lots of picnic spots on the Drayton Hall grounds if you'd like to bring a lunch and stay a bit longer.