We are a 50-something married couple with 12 cruises under our belts, so, I think we have enough experience to be objective. We have sailed on Royal Caribbean, Carnival, Princess, Holland America, Celebrity (Mercury), and Oceania. After a day or two onboard Millennium, my husband looked at me and said, "I think we've finally found what we've been looking for". After all seven days and nights, I agree completely!
Embarkation was very quick, we got there at 11:00 am, and boarded this ship 15 minutes later. Celebrity has a better system for checking people in than the others. When we got onboard, we were greeted with a smile and a glass of champagne, and escorted to our cabin. We had taken advantage of a deeply-discounted special and booked the lowest category cabin 2180 inside, hoping to upgrade at the pier, but the ship was sold out so we couldn't do that. As it turned out, the cabin was adequate for us, having plenty of drawer and closet space (and, believe me, I'm a heavy packer!) and a bigger shower than most. Our cabin steward was Miguel, he was excellently efficient and so pleasant to deal with.
The ship is gorgeous, elegantly decorated, and well designed layout. Our tablemates were interesting and friendly (they were two couples who have had 44 cruises on Celebrity each--and we gleaned their knowledge over the course of the week about how to get the best price, cabins, etc-- and, by the way, they had all traveled on the other lines, too, and they were all convinced that Celebrity has a superior product--they were retired people in their 60s).
The wait staff was very good, and the food was delicious. It was every bit as good as on our Oceania cruise, which touts itself to be "the best cuisine at sea", which was also excellent, but we paid three times as much for that cruise. The food in the Olympic restaurant is wonderful, but what really sets it apart is the 5 star service. It is a treat that no one should miss, and well worth the extra price (30.00), you can also order a wine tasting menu with the food and it is 57.00 total. We ordered three glasses of wine and it was 41.00 but it was exceptional. We also ate one night at the "Casual Dining" venue on top of the ship, it is part of the buffet area that at night they fix up with white tablecloths, you order off a menu, and waiters serve you. It was as good as the formal dining room, you don't always need a reservation, though they appreciate it if you do.
We were impressed with the quality and variety of the entertainment, actually wishing we had a few more days on board to try everything to do. We spent a lot of time in the pool area and spa, so we missed a lot of lectures, movies, and classes. The spa was wonderful, the treatments were pricey, but one of the free things to do was spend time in the Thalassotherapy pool, then go into the bathroom by the spa, where they have a free sauna, and good hot showers, and nice toiletries. Even though they did have a few specials on port days, I wound up spending as much in the spa as my cruise cost!
We went to the Cruise Critic party (which isn't really a party, just a "gathering" with coffee, rolls etc in the morning), it was interesting to put faces and names together, and sit around discussing our perceptions of this ships VS others in the past.
To sum it all up: If you're looking for an elegant ship, with lots of entertainment choices, and excellent food, this is your ship!! For us, Carnival is too "wild" (loud obnoxious kids and parents, drunks, and blasting music with dirty lyrics), Holland America too old, and while we loved our cruise on Oceania it didn't have near the entertainment options, there were times that we were bored. We also like Princess, but after two Celebrity cruises, I can honestly say they are a cut above the other mass market cruise lines.