Just enjoyed a 6 night Florida/Bahamas cruise on the Spirit. Our first cruise with NCL. Overall, we had a very good time. We have also sailed with Princess, RCL and Carnival.
We felt the ship was very beautiful, interesting, extremely clean, and well maintained. (The only exception to this would be the balconies, which often had unwashed plexiglass, and were too narrow to really recline on).
We loved the kids pool/pirate ship/water park area, and sunbathing there offers a beautiful aft view. The main pool is also beautiful and well maintained, although crowded and the water warmed up quickly, and more difficult to find a chair here.