Just returned from 10 day Southern Caribbean cruise on Norwegian Sun, and we were very pleased with our first experience on NCL.
Although this was our 5th cruise (we have used different line each time)our perception of NCL was that it was less formal than some HAL and Princess, and we certainly enjoyed that relaxed atmosphere. We did see a number of cruisers who took advantage of the "formal" evenings, but the crew were happy to accept both formal and smart casual on those evenings.
We have now added NCL to the two others mentioned as our preferred lines. The crew were great, and always had a greeting for you and seemed to project sincerity with it. The MDR was a pleasant experience, after the first couple of days, and provided a good quality dining experience with food being well cooked and the portions of a manageable size. The only negative we could give was a sligt lack of choice early in the cruise, but that aside we were delighted. we used the buffet only a couple of times and found it fine.