My husband and I just got back from a cross-country trip following Rt 66. It's pretty easy to follow, hopping on and off the interstate as need be. There are still lots of great sights to be seen. Meteor Crater is truly amazing, it's so huge. Tucumcari has great old motels and neon signs. We also stopped in Shamrock, TX, which has the Conoco station that inspired Luigi's Repair Shop in the movie Cars, and Cadillac Ranch in Amarillo, which was the Cadillac Range in the movie.
Absolutely a trip everyone should try to make at least once! We're already planning our next trip.