I don't know about traveling from Nice, but I suspect the train will take you to Milan, and from Milan you'll take a high speed down to Rome. In general, the italian trains are spectacular for their efficiency and comfort, the speed of getting from place to place. Nothing like it in America as far as I know. But they're designed for transportation, no t sightseeing. I wouldn't call Milan to Rome a scenic ride. If your thinking of Genova and Pisa, those are local trains and you'll need to make a lot of stops, it wouldn't be scenic, and it would be punishingly lone. Nothing wrong with getting to Milan or Torino and taking the high speed Frecciarossa down to avoid airport hassles if that's your fancy, but not for sightseeing purposes.