What a great choice! This is a wonderfully maintained highway, although mostly 2 way traffic, it is very driveable, and uncrowded. The terrain was quite varied as we journied westward. We would go from vast farmland, to volcanic range land, then back to farm land, then into mountains, then river valleys, etc. This is a great secondary east/west road to explore such little towns as Coulee City (just south of Grand Coulee Dam), Chelan Lake, and many other quaint towns with large antique stores, and great restaurants.
We stopped in the little town of Cashmere, WA where we ate lunch at a great 50's diner called "Studebaker Diner". The portions were enormous.....we should have split the Bleu Cheese/Bacon Burger, but I ate the whole thing myself. The Diner is attached to this enormous antique mall that must encompass 10,000 square feet. We spent the better part of an hour after our late lunch sifting through the 1,000's of items. I have no purchases to report, but would love to revisit this little town that seems to have several of these large antique malls where locals consign their treasures for sale.