We had been on The Norwegian Spirit 2 years ago and liked it. My 15 year old son likes the fact that it is a smaller ship so he'll find his friends easier that he meets and likes Norwegian because the hot tubs stay open until midnight and this together with the basketball course was "their hanging out place' which they needed because the teen club was even in my eyes VERY lame. Pictionary with 15/17 year old kids???????? Anyway the teens found each other and had a good time in spite of no good teen entertainment.(A teen disco would have been the least they could do) In the end he had fun because he did meet nice kids his age and they found stuff to do. Not a lot of obnoxious teens (or grown ups) on the ship so that was nice.
So on to other things. Compared to 2 years ago I think they cut down on things. Less staff that goes around the deck to sell drinks. During dinner it was even hard to get the waiter that serves wine. The cruise directer was barely doing any entertainment by the pool during sea days. (this is fine with me because I don't need it but if you're used to this on other cruise lines you will be disappointed) The sun is small so few lounges for entertainment at night so just be aware of this. the "free" dining rooms had no "wow" factor at all decoration wise and the atrium is very small at this ship.It's a well maintained ship and clean just without the "wow" factor.
For the rest the food is average cruise food. Our cabin was nice and clean. The staff super friendly everywhere on the ship.
So if all you look for is to relax and don't need awesome entertainment The Norwegian Sun is an ok ship. If you want to be "wowed" don;t choose the Sun.