I rode the BRP, the Natchez Trace, and a lot of other roads in 2011. The Trace is similar to the BRP in being a long, essentially uninterrupted road closed to trucks and controlled by the Park Service, but they have very little in common in terms of landscape. The BRP is mostly mountainous and has a lot of twisty parts; the Trace is fairly flat and straight. But that said, it's still a nice ride in its own way.
For pics and more info, see my ride report: