A lot of the mountain courses are great fun to play, but wouldn't necessarily be endorsed by GCA conneisseurs. I give you Keystone Ranch and River, Raven at Three Peaks, Breckenridge and Pole Creek, plus two courses south of Denver, the Ridge at Castle Pines North and Bear Dance.
My favorite might be Keystone Ranch, in some respects sort of a plain RTJ Jr. design in a mountain valley. The bunkers on the sides in range off the tee are there, but I don't care. It's walkable, it's challenging and it's great fun, especially in the morning when the clouds are lying low and the elk tracks are visible.
Tom H, I was somewhat disappointed by Spanish Bay, which I played several years ago. It was nice enough, but I had read that it played like a links course and that it was built with Watson's input to be just that. Of course, that's not accurate at all so, from my perspective, the course was doomed by high expectations.