Reviving this thread because I just saw my first 36 Flynn greens at Lancaster and Rolling Green. At the speeds they were presented (Lancaster's superintendent told me his were rolling at 12), I've never encountered more difficult green surfaces to read. The reason for this, to my eye at least, is because of Flynn's emphasis on converging slopes instead of noticeable contour and undulation.
For example, at Aronimink the Ross/Hanse greens bulge and sway like the surface of a roiling sea, with identifiable swelled mounds from which you can approximate the ball's line as it will roll across those waves of turf.
Flynn's greens, however, appeared as wide panes set at subtle tilt. The image that came to me was of drifting floes of glacial ice jostling against each other, each of their surfaces smooth and slick, but conjoined at different angles in their haphazard arrangements. For the most part, I knew which way the ball would roll, but was always left guessing as to where it would begin cascading in the direction of the prevailing slope. The putt's pace required that much more precision for the ball to get in proper alignment with the hole, to which I failed repeatedly.
Whereas I'd call the Ross greens I've seen at Aronimink and Oakland Hills South both challenging yet whimsical from their billowy shaping, Flynn's greens are staid and serious. The deceptive strength of their subtlety presents a stern test, which should come as no surprise, given that one of the early initiatives of the Philly School was to develop difficult courses to improve the pool of competitive players in Pennsylvania. More time on Flynn greens would certainly make me a better putter (if they didn't break me first).