I did it a couple of years ago. It was interesting, but don't expect to set any pr's. It is sort of a group ride. It goes all around town, showing you a lot of Nashville - Shelby Park, East Nashville, Metro Center, the Bicentennial, out to Music Row, into Belle Meade and other areas I don't remember.
None of it is hard, but with the traffic and all the turns, none of it will be fast. But that's not the point anyhow.
So, depending on your mindset, you might have a blast or be bored.
I rode the TDN last year. It was interesting to see how may greenways and bike trails Nashville has. Also, the volunteers were nice and the rest stops were good. However, all the stopping and starting on the metric route can become tiresome. I agree this is no time to set a metric PR but it can be fun if you think of it as just a "ride".