Norwegian Dawn wasn't sold out yet, and had plenty of vacancies. Rosie comes along and says I'll buy out the ship. NCL says, of course, you've got a deal. Unfortunately for those already booked. But as others have said, it happens on every cruiseline. The money talks.
Norwegian Spirit was built and entered service as Superstar Leo for the Star Lines, the parent of NCL, targeting the Asian market. Two years ago they decided to move it to NCL which is rapidly expanding. It was not built expressly for Freestyle, like the Dawn and her newer sisters, but is a very nice ship.
I've been on three NCL ships so far and had a wonderful time each time. I really like Freestyle dining, and the general style of Freestyle. I like not having to vacate my room by breakfast on the last day and being able to wait in the room till they call us to leave. Dining in any restaurant between 5:30pm and midnight. As long as I make reservations for the specialty restaurants the day I board, I get the reservations I want. We actually prefer to eat in the main dining room most nights.
The people that have problems don't make reservations the first day or are part of a large party. I don't know of any other cruiseline that tries to seat 15 or 20 people together, like NCL does. The service isn't great when they do. Have you ever tried serving a group that big and getting 20 different orders all served promptly and at teh same time?
As long as you go aboard NCL aware that it is Freestyle, and different from the traditional style of other lines, you'll do fine. I have plenty of customers who specifically ask for NCL and enjoy it.