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.
Small closet in awkward place, not much storage. 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.