Full disclosure: I have personally taken courses taught by David Hakckett Fischer, and I know several of his proteges personally.

Some parts of Hackett's work have stood the test of time better than others. In particular, he probably overstates the influence of Quaker and Northern English influence on the mid-Atlantic states, which also were very heavily influenced by German and Dutch immigrants.

His work has best been influential on the ways in which distinctively East Anglian Puritan ideologies and social systems continuted to be influential in rural New England into the early 20th century, especially with regards to ideas about education and cultures of municipal government.

There's also been a great deal of sociological work attempting to justify the Scottish origins of a reputed Southern "culture of honor", an idea which is not nearly a popular today as it was 20 years ago, but which still has legitimate supporters within some regional contexts of the Southern uplands.

Generally speaking, Fischer's work is considered a landmark in understanding the origins of distinct regional cultures of the 18th-centurny United States. However, newer work has tended to suggest that Fischer overstates the degree of continuity between 18th-century Britain and the modern United States.

More recent scholars of Appalachia like Gordon McKinney and Altina Waller have tended to emphasize the important ways in which different political and economic situations through the early 19th century have created the distinctive regional cultures. Fischer portrayal of the origins of northern Appalachian cultures has been especially criticized by Waller in her contributions to the 1995 collection Appalachia in the Making.