Haven't stayed there. But the Flybussen public transport is the fastest option other than (expensive) taxis. It only runs once per hour. Per plan, travel duration is 36 min but they can occasionally be delayed. Google Maps directions for public transport seem pretty spot-on for OSL.

Botton line: I wanted to stay here. But for late arrivals/early departures, I think the airport Radisson is waay more convenient. And I am really not particularly fond of the terminal Radisson Blu, it is a very tired property.