Johan and Rannveig's annex is a great use of a small space, and a place I'd be more than comfortable staying in for an extended period of time. As it was, it served as the perfect jumping-off point for our adventures. The bedroom loft, bathroom, and sitting area were more than enough to serve our needs as we came back home from a long day of exploring.
Though a bit far from the most tourist-oriented areas of the city, it's extremely well-connected to Oslo's easy-to-use and reliable bus network, which we made extensive use of during our stay. The neighborhood itself is quiet and seems to be undergoing a bit of resurgence mirroring that of Oslo on the whole.
Above all, Johan was always readily available using the Airbnb app to give us tips on things to see or do, where to eat, or how to get around. We got a nice bonus by getting to see SALT, the transient cultural village project located along Oslo's former docklands which are in the process of revitalization, and which Johan has helped oversee for the last couple years.