The route is neither long nor complicated; once you get out of Nagano, there's only one way to go, and even during a major holiday week the roads were not overly crowded. The climb is also quite gradual considering the elevation. If there's any chance of snow, you'll want to make sure the road to Manza is open (ask at the tourist office in Nagano). Once you get down from the mountains on the eastern side, the route is clear all the way to the big river, at which point you have plenty of road options - so consult your map and try the road of your choice. The offroad section (which goes directly from Shiga Kogen to Nozawa) comes highly recommended as one of the nicest in Japan [update: it appears that this is now paved!].