I went in the early 90s, and we saw Skara Brae, Ring of Brodgar and Maes Howe, all of which were awesome. Ufortunately, we were on one of those organised coach tours so I could have happily stayed for far longer than we actually got at all those sites. And Ness of Brodgar hadn't even been discovered at that time.

A return visit may need to be made at some point.