Naples is a beautiful city.

I have to say that in the beginning because I don't want to give the impression that I don't like it.
My mom's mother, grandma, was born there (Ischia), we used to vacation there for many years, and we liked it.

But Naples has some quirks that make it a city to be always in alert mode for...
It's sadly famous for the frauds, big and small, perpetrated in the streets, where somebody tries to sell you something very expensive (watch, cell phone, camera, leather jacket, fancy purse etc) for very cheap, only to swap it at the last second and the person buying it gets swindled and is left with a brick or a piece of garbage...
Swindling people has become almost an art form, and is celebrated even in movies... No regard for the person being cheated...
Driving is a nightmare, people drive like it's a race and the rules of the road are lightly regarded... Years ago we were visiting and I remember we had to dodge mopeds and motorcycles on the sidewalk, because that was being used like a lane of traffic. crossing the street was an adventure...

Taking public transportation is also another opportunity for thieves to rob people. In all my years of living in Italy, only once I had somebody try to pick my wallet out of my purse, and that was on a bus in Naples. The person was unsuccessful, but still.

So. be careful in Naples!
Having said that... Naples is a city full of amazing art, sights and food places! They have the best pizza (well, I like roman, thin pizza better, but I am biased) and best pastries.
The sea is still amazing, in spite of the pollution and the chemical from the local industries.
Capri and Ischia have amazing beaches, and those alone are worth a trip in the area.