We love November and December, weather wise. It’s definitely cooler and less humid than summer, less rainy too. Temperatures can vary a lot and be very unpredictable. You might be comfortable in shorts and t-shirts during the day but need a light jacket and/or long pants in early morning and after sundown. Or sometimes it’s cold. So you need to pack layers.
As far as crowds go, the first two weeks of December are usually the lowest crowds in the parks, although the parks won’t be empty. The busiest weeks in November are around Veterans Day and Jersey Week (the week of Election Day). Thanksgiving Week builds starting the weekend before and gets more crowded as the week progresses, especially Thanksgiving Day, but crowds thin out somewhat the following week.