SPDB:
Honestly not much at all! But by saying that I do not mean to criticize Brian Silva!
I can only say two possible things about the new nine.
1/ It would be immensely difficult, if not impossible, in any case, to build a nine on that topography that could in any way have complemented or matched Ross's original nine holes!
2/ Another nine holes just should not have been attempted there (if the club or Brian was in any way really trying to match or complement the original Ross nine).
The overall slope on that portion of Rolling Rock is too severe for old fashioned types of holes and architecture and a number of the new holes are "shelved" or "stepped" into the terrain (something Ross never could have done)!
Some of the views are spectacular and most of the holes do have some real interest in playability and strategy but not much like the old ones do and the new ones certainly don't look much of anything like the old ones do. But frankly, given that topography I can't see any way that they ever could have.
An architect like Ross in 1917 NEVER could have built a nine where the new nine is and that's probably what the club should have considered, if they cared about that kind of thing at all!
Apparently, there may be better ground for golf on the other side of the old nine but a Mr. Mellon would not allow it there as it might have affected his view, or something of that nature.
It should be said that Rolling Rock Club is definitely one of the most amazing clubs and places I've seen in my life! Golf is by no means all that goes on there with all the other things the Rolling Rock Club was created for. Hunting and fishing are as important, I'm sure, and always have been, as probably are dining and such or just relaxing in an otherworldly relaxing atmosphere! Riding, steeplechasing and fox hunting may have been at one time but apparently no longer!
It's amazing to consider but I was told that originally the Rolling Rock club encorporated somethng between 25,000-45,000 acres of land!
And if you want to see what real true style--old world style--is all about, in every single imaginable way, you'd have to search the world to find much to top the Rolling Rock club!!