It's not just that the road provides the best experience, there are plenty of roads like that.
Examples of that:
1- Calais to Prague: Calais-Duisburg-Dortmund-Kassel-Erfurt-Prague; almost all driving experience is 1-1 roads(1 lane to go, 1 lane to come)
2- Debrecen to Rostock: Debrecen-Kosice-Lublin-Bialystok-Olsztyn-Gdansk-Szczecin-Rostock
3- Bergen to Oslo: Bergen-Oslo(both mountain road should be seen
4- Milan to Zurich: The Alps mountain passage should be seen
5- Klagenfurt to Innsbruck: The Alps again
6- Liege to Montpellier: Liege-Reims-Saint Laurent-Limoges-Montpellier
These are the first ones that came to my mind in a second. More nice roads can be found easily by avoiding highways.