The great: It's an absolutely perfect location--literally in one of the colorful old buildings you see in every photo of Copenhagen, right on the main street in Nyhavn, above a waffle shop near the Nyhavn sign. The view from the apartment is fantastic. The metro stop is five minutes away, and there are bus lines close by as well. The apartment is large, so it is easy to spread out. The bed is comfortable and there is a good couch and a dining table in the main room; the other room just has two chairs in it and we didn't really use it.
The not-so-great: The kitchen is fairly basic, and unfortunately did not have a microwave. The bathroom is very small, and the shower wasn't great. It is just a hand-held shower and there is nowhere to hook it on, plus the curtain is so close to the wall that there is no room to stand if you pull it closed. The pressure and the temperature are fine, though. Also, some of the amenities are lacking: there was only one extra roll of toilet paper for a 6-night stay, and no hand soap. And the hair dryer didn't work very well.
Be sure you can handle a three-flight climb on a tight and uneven set of stairs.
It was very easy to communicate with the property managers--they were responsive and friendly.
Overall, we really enjoyed our stay here and the fantastic location alone compensated for whatever minor issues we had with the place. But the apartment would be so much better if these other concerns could be addressed.