I loved staying at Espen's Airbnb. The apartment is accurately depicted online. Everything was spotlessly clean. Even though his apartment with his family shares a wall I could not hear them. I am a light sleeper and I was able to sleep until mid morning if I chose to. When I first got there I was worried that street noise and people walking by would keep me awake, but it's an extremely quiet neighborhood and I was able to sleep soundly without interruption each night.
I would say it's good 20 minute walk to certain parts of the city but I wanted to walk. I would say walking to the theater district or the palace would be a little too time consuming so use the public bus system. When I did use it I found it to be fast, timely and efficient.
Buy yourself an Oslo city pass. You get into most of the major attractions and it covers all of your public transportation. Completely worth the money. Plus there is an app for it that you can download and use on your phone. You can buy the pass with it as well.
I happened to be there on their National Day, May 17th. Since I was traveling alone Espen invited me to join him and his family to enjoy part of the day together. I was even invited into their home to share dinner with them that evening. I really enjoyed meeting their entire family. They are great people. I highly recommend staying here if you can.