On our last three HAL cruises, my husband wore his slacks with a sport coat and tie for formal nights, with no problems or issues. I have a "little black dress" for formal nights. Other nights are slacks and a polo/button down shirt for him and a casual dress for me - only because I don't have casual slacks/trousers. Norwegian will be much more casual, but formal night is still formal night - whichever line you choose. For dining in the dining room, look to at least a jacket and tie for him, nice dress/pant suit for her.