Since Tony mentioned my name, I guess I will reluctantly dive in.....
I wonder how Forrest determines the ratio of plans to field. I will agree with Tom D that great greens become great in the field. I almost always draw plans, but the final tweaks often determine greatness. Not always.
First, lets determine what "great" is? For some, its determined by the contours, with random contours being the only test of greatness. However, in the right case, it could be a plane slope green in conjunction with the approach that makes it great. Or a small, flattish green whose greatness lies in how hard it is to hit.
For me, its determined in part as part of the golf course composition. For example, a flat green might be great if put between two rolling greens as a change of pace, and if it fits the hole, even if in and of itself, it may not be great.
Even a manufactured Seth Raynor green can be great if it inspires someone to play golf and makes a statement. Many different types of greens can make a statement - an elevated green inspires fear on the approach, a highly contoured green inspires fear on the putt, while a flat green inspires doubt, etc.
I also think there are some greens that are great (or at least very good) for their role., ie, a high play public course doesn't want the tricky contours but needs a certain size to survive and that type of green might be great - or at least a great match to its intended purpose.
In fact, in all of the above, perhaps the answer is how does it fulfill its intended purpose? And there are a lot of ways to do that and be great.
To morph over the wandering discussion, most folks - including some professional golf course architects - don't have the artistic vision to create something really great. A lot of designers can get it close by copying what others do, but if you see a green you like, it was probably designed by someone with talent and vision, whether on plan, on the dozer, or whatever. You can't explain it, but you can feel it.
I will side with Forrest in the debate whether any one on this group board could design a great green on their own. If only a portion of the people so inspired to devote their lives to the study of gca and invest their time and money to do it get it "right" I can't imagine others who have sacrificed much less could do it better in even half the proportion. It could happen, to be sure, and has, so its not black and white, but the % would be very, very low.
Just my $0.02