Someone else called Civ "lightning in a bottle" and I'd have to disagree because of how many other great games Sid Meier has to his name (Pirates, Silent Service, F-15 & F-19, Railroad Tycoon, and more). It must be concluded that it was his skill rather than just a singular moment of creative genius, but I guess it's fair to say that Civ was the absolute pinnacle of his career.