You will love the Serenity. Food and service is really top notch. Don't miss the mushroom soup or osso buco at Prego. If you like Asian food or sushi, Silk Road is wonderful. Also, if you don't want to go the the formal dining room, Tastes, the more casual restaurant, is open some evenings for dinner. There are options for both breakfast and lunch other than the formal dining room. If you're a late riser, there's the Lido and if you're a really late riser, the Bistro is another place for a good cup of coffee and things like bagels, danish and fresh fruit.
Crystal is one of the most formal dressing ships in the industry. You will find that 98% of the men wear tuxes or dinner jackets and the women go all out on formal night. Lots of sequins and long dresses, evening pants with sequined jackets and sparkly cocktail dresses. Informal nights the women wear things like dressy dresses or dinner suits. Think along the lines of a St. John (even though you don't have to wear that line, but that's the basic idea of what the women wear) or a dress you would wear to a more dressy wedding. Another thing to know, people don't go back to their room and change into other clothes after dinner. On Crystal, if you're going to be in any of the public rooms after dinner, Crystal asks you remain dressed in the code of the evening for the entire evening. During the day, you will find all types of clothing. I mostly wear capri pants, tops with sleeves (so I can go into all the churches) and comfortable shoes. You will see the older couple who wear fancy clothes even during the day (why, I don't know---I just can't see wearing a pantsuit and pumps to walk on a tour).
If you like desserts, that's a strength for Crystal. I'll give you a couple of things to ask for. Talk to your head waiter and tell him you would like a special dessert the next evening. I've asked for chocolate souffle, bananas foster, and my absolute favorite--Saltzburg Knuckle (it's absolutely heavenly, fluffy meringue floating on a sea of vanilla and lingonberry creme sauce---YUM). They will also prepare tableside dishes for you, so don't be afraid to ask for anything. I usually ask for garlic shrimp over linguini for dinner one night.
While some might find the ship's tours to be rather expensive, Crystal does a great job in that area. They limit the number of persons in each group and the guides are very knowledgeable. I usually hire a private car and guide because I'm disabled, but I've been a more than a few Crystal tours and they are great. The concierge can arrange private tours for you if you give them enough lead time.