My experience with NCL on the Norwegian Gem.
To give you a little background on the people involved, my wife and I are both in the 30-35 year old bracket, full time working professional people. We are in no way formal and generally enjoy a casual atmosphere; more 'jeans and t-shirt' than 'where's my tux?'.
We've cruised three times previously, always with Royal Caribbean. We've been to the Caribbean and the Mediterranean, leaving for these places from Spain, New Jersey and San Juan ports.