We went on the Greek Islands tour on the Emerald Princess. It was my first cruise and my wife's third, my wife and I are in our twenties. We had a great time and I found it to be a great introduction to cruising.
Dining: The food was great. We ate at Da Vinci's every night with the anytime dining option. Don't even bother with the buffet, it's nothing compared to the restaurants. It does a really nice breakfast also. The food was what I'd expect from a restaurant charging $70 each for dinner. One great thing is that if you have only half a bottle of wine they will store it for you for the next night - at any ship restaurant just tell them where you last had it, and they will send someone to get it for you. If you are in a rush try to get there early, so you can get a table for two at the start, otherwise it is quite a wait to get a solo table, or just join a group table, but then it will be quite a slow process. The wait staff were really good, and were able to recommend things and help us with any requests.
Entertainment: The shows at the Princess theatre were pretty good. There was a bit of an art to getting to dinner at the right time that you can leave and make it to the shows before it fills up, but without getting there so early you waste time waiting. They had good singers, dancers, comedians and even a hypnotist show.