I've been to Duke Chapel, but have unfortunately not heard the organs in person. I do have several recordings however.
So nice you got to play - isn't it an awesome feeling of power to play in such a space, on such an organ?!
The Flentrop is impressive (the casework is similar to that at St. Bavo Church in Haarlem, Holland - which is even better)! But I must confess I am much more impressed with the

enormous[/b] old Aeolian organ at the front of the chapel. Aeolians are quite rare, especially one of that size (they specialized in smaller home organs for the very wealthy). This is said to be the last Aeolian built before the company was absorbed by Skinner, resulting in the fabled Aeolian-Skinner company.
It once had an echo organ, which was unceremoniously dumped when the new Flentrop was installed.
It's nice to have a huge, historical organ from a foreign country, but I do hate to see something of value from our 'golden age' get pushed aside. Hopefully, the 'powers that be' at Duke realize what treasures they have in both instruments.
Actually, there are three organs in the chapel! There is a historical model of an Italian organ by Brombaugh.
For the whole Duke organ story, look
here!