I previously sailed on the Mariner of the Seas which has the identical floor plan to the Navigator, and I really enjoyed that cruise, but I was disappointed that the Navigator was not as good. I'll comment on a few areas that made the most impression.
Embarkation: We got to the terminal around 11:30 am and there was practically no line. We were on the ship and in the buffet in maybe 30 minutes. That's the way to go!
Food: Just average at the beginning of the week, but it got better as the week progressed, especially in the MDR. Desserts were generally good there, better than at the buffet. We had first seating which was a bit early for us some nights. One annoyance was that they only had white bread rolls at the meals, which I almost never eat. We tried to ask for whole wheat or whole grain rolls and were met with confusion (and more white rolls). Finally the headwaiter got some nice bread from the buffet (why did they only have it there?), which was just what we wanted, and from then on we had a few slices available every night. In the buffet the vegetable selection and salad bar could have been better. We were surprised that the buffet closed so early every night (9 pm). On Princess we could go do a run through the buffet after the show and see if we missed anything that we wanted to try. We liked Cafe Promenade but they needed more variety in their food offerings, especially the desserts.
Lounges: This was the biggest disappointment. My boyfriend and I do a lot of partner dancing (ballroom, nightclub 2-step, swing, Argentine tango) and we love to dance on cruises. This ship had HORRIBLE floors for dancing. Nearly all of them were tile instead of wood, and every single floor was incredibly sticky so you couldn't turn or pivot on them; very bad for dancing since forcing turns can cause injuries. This was not the case on the Mariner so I don't know what they did to those floors. We and other dancing couples we met on the cruise complained about it but nothing was done until the last night. Also, the bands didn't start playing until quite late most nights, after 10 pm sometimes, and they all seemed to take breaks at about the same time. Also, the bands repeated their music a lot, especially the one up at the Cosmopolitan that seemed to play the same set of music every night. We were pretty tired of the songs by the end of the week. They also played too many of the same type of music in a row. Every good dance band knows that you need to vary your music!
Cabin: We had an inside cabin, and with the beds pushed together, there is almost no room to get around the end of the bed due to furniture being right up against the end of the bed. I've never had that problem on any other cruise ship before. I like the shower with the shower doors though; much nicer than the curtains on Princess.
Overall a good cruise, but I think we preferred our last cruise on Princess to this one due to the above issues.
It was nice to get a chance to visit New Orleans though. We stayed 4 nights after the cruise and enjoyed seeing the sights there.