Jason Topp says: "It is interesting to me that people seem to be equating "penal" with "tough." I have always understood the term "penal" to mean that there is one way to play the hole and you either succeed or fail."
I may fall into this camp to the extent that in my definition a penal course under normal conditions is always tough whereas there are tough or difficult courses which may not be necessarily penal (Yale, Bethpage-Black, Colonial).
With very few exceptions, there are multiple (more than one) ways to play a hole. #16 at CPC can be played with medium and long irons to the left, a fairway metalwood to the hole, or a driver to somewhere on the very large green. Even #17 at the TPC- Sawgrass can be played with a variety of iron shots and even just a putter.
The main differentiation I make between penal and strategic design, other than the latter offers more options, is the consequence of failing to execute the chosen shot. A penal hole or course penalizes that shot much more severely (reaching into the pocket for another ball), whereas the other still leaves some hope for recovery.
Bad rounds on penal courses generally result in very high scores (high 80s, low 90s for a low to mid-single digit player). On other courses, the same player can be hitting the ball badly but score closer to his average.
Subject to the caveat that it is dangerous to make broad generalizations based on limited exposure, Winged Foot- West just seemed relentless in punishing even the marginally bad shots. With the dense rough, difficult bunkers, and complicated greens, my objective on some recovery shots was just to save bogey, nevermind thinking about par.
The five finishing holes, I think all played as par fours for the US Open, are nothing short of brutal. Mishit the drive in any of the last three and it will cost at least one stroke. Miss the green on the wrong side, again, it costs at least one stroke.
Regarding Spyglass, with the wind blowing the stretch from 2 to 5 can be a nightmare on the scorecard, provided that you are playing by the rules and marking down all strokes. #3 in a swirling 20 mph wind is frightening, as is #5.
The inland holes require distance of the tee as well as precision. In the normal soft conditions, the ball doesn't go anywhere and there are a lot of really bad places for the forced second shots to find.