Greens with great combination of dramatic and subte internal contour do it for me.
However it is hard to select an individual feature because architects that get this right (Doak, MacKenzie, C&C, Maxwell, Flynn), tend to get most other things that I like right too - width, naturalness, variety of hole length, short game options.
Conversly a course with flat greens will generally be long, monotonous and unatural looking. And a course with tricked up greens will be over shaped and over bunkered as well.