I admit to a dislike of Naples. I lived there four years as a little girl and went to Italian schools there. Naples and I just don't mix.
This is not to say that there isn't plenty to see in the city and its surroundings. The Archeological Museum alone (in the picture, a statue from the museum) would warrant a trip. But if you're a first-timer to Italy, like Seth, and especially if you think you're only likely to make it to Italy once, I would not give it priority. However, if you will be visiting Rome (another city I'm not too fond of), be aware that Naples is rather close (about two hours by car) and that if you have the time and a special interest, a day or two in Naples may be a good idea.