I don't know about anyone else, but traveling through Navajo country was kind of a depressing experience. Last year, I was in Moab, UT and drove south on Highway 191 all the way down to I-40. The landscape was barren, and it seemed like each town was poorer than the one before. In one town, they had a herd of sheep walking and grazing along the side of the highway. I damn near ran over a couple of them. Nobody bothered keep them fenced in. I'm surprised there weren't sheep carcasses all over the place.
It might be worth it to stop by the Meteor Crater just west of Winslow. The admission fee was kind of steep, but its a cool place to visit once in your life. Its amazing to see how huge the crater is in person.
When you go to the Grand Canyon, try to get there a little early. When I was there, the line to get in was long, and parking was a real bitch. I think it took me at least 20 minutes to find a spot. You might want to bring your own lunch and snacks with you. You're gonna be starving after walking around all day.
I love the drive from Flagstaff to Phoenix on I-17. One of these days I'll take the scenic view through Sedona like everybody recommends.