Great location in a traditional building. It gave us the feeling that we were living like locals. The attention to detail inside the apartment leaving shampoo, soap, hair-dryer etc was a nice touch.
Allesandro met us and gave us some really useful background info about Napoli and Angela also provided some brilliant recommendations. There are good restaurants / cafes within easy walking distance. The pasticceria opposite is fantastic for breakfast, and Oliva pizza is worth a visit.
Some practical stuff for other visitors:
A taxi from the airport to the apartment is only EUR18.
Stazione Centrale (train station) is 15 mins walk.
Pompei is worth a visit and is only 30 mins and EUR3 on the train (not a typo - it really is 3 Euros!)
Trattoria Da Pasqualino Di Cappella Salvatore was a nice restaurant we visited. Really friendly staff and great food.
The best thing about Napoli, as Alessandro said, is just to wander and enjoy!