Thendara is one of my favorite Adirondack courses. I love that Ross front nine. Gives me a chance to score, and on foggy mornings to watch the deer play. Good preparation for that tight and interesting back nine. It is my understanding, from info I've seen at Thendara was well as the Cornish/Whitten book that William Harries did the back nine. Compared with the front, it is a very challenging nine with some terrific golf holes--#11, #15, #17, and #18. It's a neat place to play. But, I would not go there looking for a great example of Ross design.
Teugaga has been mentioned. That is one of my favorite courses, anywhere. Wonderful terrrain and routing that create a distinctive character for each hole. Terrific green sites that are beautifully placed and contoured. A great experience. And, after golf, enjoy some lunch on the patio overlooking Delta Lake.
Ed