Even though Rome is a very popular port on cruises, and it is even the starting/ending point for some cruises, there is not actually a cruise port in Rome. Cruise ships port at Civitavecchia, which is about an hour away from Rome. Most shore excursions will take a 1 hour bus ride into Rome. If you plan to do Rome by yourself, there is a train station in Civitavecchia with frequent trains into Rome.
Rome, as a cruise port, is not convenient but it is worth the trip. The train into Rome has stops near some major attractions and it is easy to walk from those to the metro and back to a train terminal so that in the end you can see most of the major sites of Rome in a day if you plan and map out your course Before You Go.