I have been on a lot of 66, I am a HUGE fan of it. I even had one of my senior photos last year on that road. Yep, drove all the way to missouri to do it too!
There are bits and pieces of it. Most of the remaining highway sits in the southern states.
If memory serves me right, sections of 66 were not paved. You had long stretches of no gas stations. And in the 40's and 50's a lot of wierd stuff popped up along the route. (hotels, trinket stores etc.)