Overall, a fantastic stay in Naples! The location is superb - an absolutely gorgeous spot right next to the castle and on the water. Easy walking distance to restaurants (we walked to the famous Pizzeria Brandi - past Piazza Plebiscito and it was only about 10-15 min by foot) and the port with the fast boats to Capri (Molo Beverello port was about a 15 min walk). It's so nice to walk down the causeway past the marina and all the boats and the gorgeous Naples coastline each night when coming back in from a day of exploring.
The flat is surprisingly spacious - we had 3 adults and 2 kids and felt comfortable the entire time, but the best part were the THREE bathrooms, so helpful when traveling with a family! The kiddos loved the hammock and watching the people stroll by on the street below.
Only drawback (but not enough to reduce the number of stars) was on Saturday evening, the music from the bar downstairs - even with the windows closed - was pretty loud (bass booming) and kept the less-heavy sleepers up a bit. But every other night, was perfect and peaceful!
Would recommend to friends - I would stay here again for sure!