Pompeii was an easy side trip from Naples and something I definitely wanted to do while in Italy. It was really cool walking along the streets and going through the houses of people from over 1000 years ago. Something that was funny was you can see how they had granite and marble countertops in their kitchens even then. It just goes to show some things never change.
One thing I highly recommend you do is to get a map and the audio guide before entering the site. This is because the city is built almost like a maze because of the sections that they close for restoration. I had a map but because there were so many streets that were closed it was incredibly hard for me to find specific places of interest. If you have the option to go with the tour I would highly recommend it.