Rode from Arco to Missoula. This a good road for scenery as over its long stretch it goes through pasture valleys, along rivers and over a pass. Some nice twisty stretches south of Salmon, and then either side of the pass.
There ought to be some adjective between "4 : Pleasant" and "5 : Spectacular." I gave this road 4 stars (Pleasant?) but it's just short of spectacular! Chalis is a small curve in the road with decent rates and camping. Salmon is a great little town with some history, gas and good grub. Along much of the way the road traverses back and forth across the Salmon River winding through forests and along wooded canyon cliffs. North, it drops you off near Missoula right at the entry to Lolo Pass road, Hwy 12 - perfect!!
A very nice empty road that has many nice corners, takes in a national monument and is pretty well surfaced. Well worth a look.