Alliebird -
I've played a few William Mitchell courses:
Mt. Pleasant CC, Boyleston MA, 1955
Kutsher's CC, Catskills NY 1958
Tarry Brae GC, Catskills NY, 1962
Thomas Carvel GC, Pine Plains NY 1968
McCann GC, Poughkeepsie NY, 1972
Mt. Pleasant is the only private club in the bunch and it is quite good with some unique and memorable parkland holes. Nice creative routing, too. It's well respected in MA and I believe it has hosted the Mass Amateur and perhaps even the Mass Open. You should check it out near Worcester if you ever get the chance.
All of the Mitchell courses I've played are in somewhat hilly, rustic and heavily treed settings. They use the land very naturally (not much visible earth moving) and they are not "polished modern courses" if that makes sense to you. Natural beauty is favored over flair, and there are good golf holes on all these courses. Big, round fingerless bunkers. If Mt. Pleasant is the pick of the bunch, Carvel is my least favorite and I wish one of the nines (the one with holes situated mainly on the side of a barren hill) would sink into the molten rock at the center of the earth I hate it so much.
Kutshers and Tarry Brae are very nice, quiet rounds of golf. Great smells and nature sounds. Very enjoyable but not exceptionally well maintained. McCann is a muni and I cannot remember any holes since I've played it only one and it was years ago.
Hope that helps. Let me know if I can help with additional info.
Greg