Apartment is good - clean, good size, excellent location near station (even if this isn't the nicest part of Oslo, it is a good base from where to get around a reasonably small city).
Main problem was check-in. No-one on reception when I arrived - only a mobile phone number stuck on the door, but my phone would not work. Turns out the keys are left in a safe deposit box for you, but I don't know why the company can't tell you this before arrival.
We had a wunderfull stay, nice wether en a lot to do.