Jonny,
I'd agree with Brian...
I, together with some of your other illustrious forebears (well, last years students anyway!) played the PGA Centenary Course (as it's now called) only yesterday. By the way, to do a comparative analysis of it with the Kings or Queens would be an extremely interesting topic for an essay!
I would say that whilst generally Braid had by far the better ground to work with, Nicklaus Design did a relatively good job on the terrain they were given. The Course is undoubtedly composed of a series of MAJOR compromises. (There's some horrific walks between greens and tees - although our walking three-ball was eventually invited through the cart-riding four-ball in front....)
The routing is quite convoluted and, spread as it is around the Estate, fails to provide the Course with any real 'sense of place'. We certainly debated the choice of it for the 2014 Ryder Cup over so many other possible venues.
There's loads more character in the older courses, but again that is largely a result of a clever routing through some really wild post-glacial terrain and the selection and subsequent brilliant realisation of the greensites.
All in all, Gleneagles though must remain as one of the special places in the World in which to play golf. Spectacular!
FBD.
PS If you'd like any further info (or maybe some cheap golf!), I'm only across the water in Fife!