First, a little clarification, it is not my first time in Oslo, I have a few friends in there, and I know how the housing situation is as well as the regular flat sizes (small, compared with other cities in Europe), now, that being said, we stayed at Johan's for 4 full days and the flat and the area are very good and absolutely recommended.
We could walk to the center if we wanted to, or take a bus/tram (they are both very close). Also, there are many restaurants and bars in the area.
When it comes to the flat, it has absolutely everything you need, full equiped bathroom and kitchen, comfy sofa, nice tv, and a nice bedroom (some might say is small, but again, having been in Oslo other times and seeing other houses and rentals, believe me, it is not).
And last, even though I did not met Johan, he was always there being responsive, answering every question, offering late checkout, etc, and the check-in was effortless.