Tom & Jeff,
I was thinking about NGLA and GCGC in the context of a challenge that's fun but not overwhelming.
I don't see either course as "difficult" when compared to Winged Foot West.
Even Shinnecock, when played from the appropriate tees, is a challenge that's fun to meet, but not overwhelming.
Aside from OB and lots of water, isn't distance "THE" catalyst that creates "difficulty"
There are relatively short courses, such as Montclair, that are difficult to score on, but, the topography, with four nines on the side of a fairly steep hill, create much of the difficulty.
The more I reflect on it, "distance", "yardage" seems to transform a manageable course into a difficult course.
I happen to like what I call, "sporty" courses, courses that aren't of championship length, but courses that are a rung or two above your average local course.
I also consider ANGC from the Members tees, a "sporty" course.