First, the cruise I went on had a couple hundred other students from the University of Florida, as it was our spring break. I'm sure I'll see some negative reviews from people that my fellow students annoyed, so I apologize in advance for any problems we may have caused you. I'll try to keep my review focused on the ship instead of the passengers, so that it is useful for all future cruisers.
This was my first cruise, so I can't compare the Spirit to any other ships, but I definitely enjoyed my cruising experience. At embarkation, although there were some lines, it wasn't any worse than getting on an airplane. Once onboard, the ship itself was amazing. As I had read in other reviews, everything was always spotless. The casino had plenty of room, Moulin Rouge was really nice, and the pool area on the top deck was awesome.
FOOD: I only ate at the free restaurants, which I had heard mixed reviews about but I thought they were fine. The Blue Lagoon has good burgers, and Raffles is a decent buffet (although there was less selection than I expected only three or four main choices, a few side dishes and a sandwich bar). Windows had pretty good food, not excellent, but close. I always arrived for dinner early enough (6-6:30) to get a table right away, but generally when I left there were a lot of people waiting. The service was a little slow, but if you're not in a hurry it's fine. Some of my cruise-savvy friends said that the service was much better on a traditional cruise, but I though freestyle dining was fine. I might try a traditional cruise next time just to compare.