cruise ships look very unstable to me. They are shallow in order to visit tourist ports like venice and amsterdam) and have a huge air draught. But I wouldn't know what their stability curve looks like. I can't imagine a cruise ship popping back up from a 180 degree knock down simply because the air draught, massive superstructure , and their width is so enormous.
Bear in mind that the stability curve will depend on the distribution of weight within the vessel. Cruise ships will have enormous weight low down, in the form of engines, fuel and water tanks, and the myriad systems needed to run the ship, and relatively little weight high up (passenger cabins are mostly air). They'll therefore get pretty good stability, though of course they won't recover from a 180 degree capsize.