My experience was amazing. We went down a bike bath some 44kms asphalt and 22kms gravel. The scenery is amazing, with lush vegetation and waterfalls going down the road, you have to pass across rivers, etc. The road is dangerous with many cliffs hundreds of meters high, so you have to stay focused during the descent, in any case I will remember the many animitas and crosses that are along the way. Take a good camera.
To call the path connecting La Paz to Copacabana a road is lying. The winding path has no shoulder, no signs and is very narrow. But, it's incredibly beautiful. Most of the time it runs along the great Lake Titicaca, and when it does, the undulating landscape is dotted by humble cottages surrounded by gardens. The real adventure begins after an hour and a half in the village of San Pedro. The village is along the Strait of Tiquina and you have to get off the bus to cross it on an 18th century raft. Passengers cross in a brightly painted boat. Once on the other side, you have to walk a few yards to get another bus. At these altitudes you have to be careful, because you're brain might not be thinking properly and you might get on the wrong bus. I clarify because it happened to me.