This itinerary starts in southern Norway, despite the fact that the south end of the route is actually in Denmark. This is due to convenience; only a tiny part of the route is in Denmark. If you are in Denmark, however, a ferry goes from Hirtshals(the last Danish town on the route) to Kristiansand (the first Norwegian town).
The road is rather ferry heavy, due to the many fjords it crosses, few of which are bridged.
Norwegian roads in general are of low quality compared to roads in most European countries. The only motorways in the country are in and around the largest cities, and mostly in the flat eastern parts of the country. E39 is motorway first in the Stavanger-Sandnes conurbation, and later in Bergen. Elsewhere, it almost purely consists of two-lane (one in each direction) roads - sometimes worse and sometimes better.
Keep in mind that long stretches of the road go through desolate areas without towns and petrol stations. It is therefore necessary that your car is in good condition and that you are never close to running out of fuel. While E39 is a relatively busy road, being the main road between Bergen and Sogn og Fjordane, it may still be difficult to get help in case your car breaks down. Cellphone (GSM) coverage is of varying quality, but generally acceptable. There is G3 (UMTS) coverage in most towns above a certain size.