On our Med cruise in 2016 we got a stop at Marseille instead of Villefranche and DCL ran a free shuttle from the port to the city and back again. It was okay from the ship, but I remember coming back was a bit of a free-for-all! Marseille is a nice city though (don't be put off by the port area!), the area around the harbour was particularly nice.
Hope you have a great cruise!
The pickpockets are in any city in the world -- just keep your wallet in your front pocket and use a passport pouch in your shirt.