HI Like the others we are frequent NCL cruisers. The order of the day is what you want you wear. I would say that on Formal nights (usually one night in seven) the main restaurants like Gents to wear a jacket .My husband got turned away once! as he only had slacks and a short sleeved smart shirt! and we hadnt realised it was formal night. No problem though there are so many restaurants to choose from you just dress appropriately for where you want to eat. Dressing formally is fun and all the crew do on formal nights although over th years it seems that only about 50% do now . It has declined over the years.
We have travelled 4 times with norweigian cruise lines all norwegian cruise ships are the same it is entirely up to you what to wear and when, however shorts and vests-t-shirts are not allowed in the main dining rooms but are okay in all the other bars and casual restaurants. There are normally 2 formal nights where again it is optional if you want to dress up or not, we did and it was great, most of the guests do. Have a fantastic time, I am looking forward to our next norwegian cruise later this year.
We have cruised on the Jewel twice and dress code is entirely up to you, well almost. depends on the restaurant. In the Garden Cafe pretty well anything including jeans, shorts etc but other restaurants on board and there are ten, its better to be at least smart casual. We have done the DJ bit but these were special occasions for us, and why not. Mostly we have dressed shirt, short or long sleeved & good casual trousers but tie unnecessary/dress long or short etc. Smart. Its as if you would be going to a reasonable restaurant on shore - no jeans and with deference to the lady. NCL operate Freestyle and it works. I hope this helps.
Have cruised 10 times with ncl - all ships have no formal dresscode but avoid jeans in any but buffet dining at night. Depends on the cruise as to level of formal dress. American passengers tend not to bother - some will put on DJ for a photo then change for dinner. Bassically it is up to you as daily planner does give a suggested dress code but less bother than on other lines.