Let's try this another way. Why should you NOT try NCL??
Personally I have sailed them 5 times over an eleven year period. Given your most recent cruises I think that you would most enjoy NCL Sky or the upcoming Sun. But I always say that everyone should try the Norway at least once, for a taste of cruising of old. Unfortunately, she is not in the prime of life now but she certainly offers a cruise experience that is quite different from most. Just be sure to avoid the coffin cabins!