So far, knock on wood, I have not met a cruise line I didn't like. I like all of the ones I've tried and certain things more on one cruise line and some things less than another.
The things I liked about our NCL cruise was the fact that I got to eat at a different restaurant every night and try things I usually wouldn't try at home, either because it isn't nearby or I wouldn't be that brave without the backup plan to try something else if I didn't like it. I liked the shower with the sliding glass door. I liked the unique asian style of the Spirit. I loved the kids facilities, and the area on the buffet devoted strictly to kid type food.
We would frequently take the kids to eat dinner at the buffet around 6:00 p.m. then let them go to the kids club while d/h and I would enjoy a romantic dinner for two while they played and had fun.
There are also things I really dislike about NCL, but the good far outweighs the bad. I also like Carnival and RCCL. They're all a great value and I would never hesitate to cruise with any of them.