DH and I are in our mid-thirties, no kids. This was our second cruise which we took with ten other members of our family.
Overall, we had a fabulous time. As others have said, this ship is an engineering marvel and it is new enough that it still sparkles. It's really quite impressive when you see it the first time. Embarkation was a breeze in Ft. Lauderdale and we went from the curb to inside the boat in about a half an hr.
The passenger load really is quite international and RCL must do a great job of marketing this ship overseas. The advantage to this ship is that there really is a little something for everyone. The shows were Broadway-quality and we especially enjoyed Hairspray, Oasis of Dreams, and Come Fly with Me. We both liked Amy the cruise director and felt she did a good job. The food in the MDR was superior to that on our last Celebrity cruise. Both of our wait staff were very personable and did an excellent job with the dinner service. The roast beef sandwiches in the Park Cafe are as good as advertised and we had them almost every day while at sea. We met the Captain riding through Central Park on a bicycle one day and appreciated the gesture of accessibility.
With that many people on board, the downside is that we felt the elevators were nearly always crowded and the pools on sea days were crammed full of people. The solarium, while beautiful was extremely hot. The service was mostly good although there were a few people that seemed unhappy or irritated (not that I can blame them with that many people week after week!). We wished that there wasn't such a push to upsell things on the ship, but understand that cruising is a business and that this is one way they make money. On hint for those with the soda package is that there are self-serve soda machines on deck 5 on the promenade near the Opal Theatre available 24 hrs a day.
We used the WOW phones to keep in touch with our group and while the voice feature didn't work perfectly over the Wi-Fi system we felt they were very reasonably priced at $30/phone/week. The phones really enhanced our experience by helping us find each other and spend more time together as a family. The text messaging on the phones works fine and there is a locator feature that helps you locate the other members of your party.
Disembarkation was also pretty painless. We used the valet luggage service for $20/person which I highly recommend as FLL will not let you check bags until 3 hrs before your flight.
So in summary, we had a great cruise. We are not sure we would do Oasis class again due to the crowds but we would do RCL again and would recommend this cruise especially to families, groups, and to people who enjoy great entertainment and food and we did overall have a fabulous, fun filled family vacation.