The Mariner is a great ship with a lot to do. We had the benefit of being the third cruise after dry dock, so everything seemed very fresh still. My previous cruises had been on much smaller ships, so I was looking forward to enjoying the promenade and the greater variety of scheduled activities. We loved being able to grab quick snacks at the Promenade Cafe (great breakfast pastries and desserts) and get a drink pretty much anywhere. The adults-only pool section was truly adults only, and very quiet. I never felt like we were two of thousands on the ship, since we'd see the same people all the time. It seemed like a pretty intimate trip albeit on a huge ship.
We had one lunch at Giovanni's Table, which I highly recommend. It was relaxed--a change of pace from buffet lunches--and the food was delicious. The desserts and steak were a little disappointing, but the pasta and appetizers were excellent. The food in the MDR was great, although a lot of the appetizers were repeats almost every night. Everything was definitely geared more toward American palates, as we loved almost everything we ate and our German tablemates were not very impressed.
The real standout of the ship was the crew. The activities staff was PHENOMENAL. We spent every day playing (and winning!) at least one game of trivia with Scottish Dave, Katie, or her husband (I forget his name). The Italian speaking activities staff members could be hard to understand, especially in a trivia game when precision is sometimes key, but the next cruise would be filled with 80% Italian speakers so it made sense that they were on board. The servers at the Schooner Bar were excellent, and we made sure to tip them well. We adored Mohammed, our assistant waiter in the MDR and often our lunch waiter in the Windjammer. He had great stories and information about the ports, and we learned a lot from him about his home country, Tunisia. I would never have been interested to visit before, but now Tunisia is on the list of places I'd like to go.
The entertainment was a mixed bag. The ice show was amazing, and we also thoroughly enjoyed the Motown tribute act. The Royal Caribbean singers musical-style show was weird; the singers were great, especially Sarah, the main female vocalist, but the story was strange and hard-to-follow. We had fun at the '70s night on the promenade, and were sad that we fell asleep before the pirate parade (jet lag on the first night). I thought the shadow puppet act sounded boring, but we caught it on RCTV later and it was mind-blowing! We walked out of a terrible comedienne's act (she billed herself as Charo + Joan Rivers, but she was nowhere near either), and might have different thoughts about the comedian/magician if the show hadn't been stolen by one of his volunteers, who happened to be our MDR tablemate.
We only went on one Royal Caribbean excursion, since the Palace at Knossos was almost three hours away from port. We also did a private tour with Hakan Bozdag, a very knowledgeable and entertaining guide in Kusadasi/Ephesus, Turkey, for about $40 pp (vs. $225 for a similar RC excursion, although their's still didn't include as much as we did). In every other port, we walked or took public transport--and usually beat the huge cruise ship crowds at 1/10th the cost of an activity or less--which I highly recommend in the walkable cities of Europe.
We only some minor issues, but in our eyes they were more positive than negative. An outbreak of norovirus on the previous cruise meant we were delayed in getting onto the Mariner. But, since we flew into Rome that morning and booked our transfer through RCI, they threw in a free tour of Rome to kill a couple hours. My husband had never been to Rome, so he was quite happy that he had the chance to see the Coliseum and walk around Vatican City, at least for a short while. Also, at our VERY organized embarkation, we were told that the port days in Crete and Athens had been switched. This worked out much better as there was only one other ship in Athens the day we actually went, and there would have been four or five others on the original day. (As far as I know, there wasn't a norovirus outbreak on our cruise, although someone did tell us they came across some major, abnormal disinfecting work going on on a lower deck.)
All in all, I highly recommend the Mariner of the Seas and look forward to our next cruise on a Voyager class ship.