This should be a 5 star property - it has a lot going for it. But several issues, detailed below, knock off a star.
The location is great, on a small square on the main drag near the eastern end of historic Napoli. An easy walk to so much, including the train station. The apartment is on a high floor with lots of natural light coming in through huge windows, and super high ceilings. The windows are high quality - though its noisy outside, it's quiet inside. The apartment has a great spacious feel. Elevator works.
Now for the bad. The upstairs bathroom accumulates sewer gases. If you leave the door open, the whole place stinks. If you close it, the bathroom is barely usable. The listing shows a dryer - there's no dryer. The bedding is 3rd rate, and the beds in the 2 smaller bedrooms are terribly hard. Water pressure dismal. Just one set of keys. The host is superficially friendly, but becomes aggressive and obnoxious over the slightest.