The Mariner is really the perfect size ship. One would have never known that there were over 3,000 souls on board, and you didn't have to hike a mile to dinner and mile back to the show. The ship is clean, well appointed and the staff is fun and friendly. We weren't too keen on the price tag for a balcony, but found the Promenade room to be a nice option.
My previous cruise on the NCL Spirit wasn't exceptional, but SOME of that was my fault. Our group didn't participate in any activities, opting to instead sit in the lounge. The Mariner had some GREAT activities, like trivia, silly contests on the pool deck, great shows, and of course, The Quest (youtube it if you don't know). My friend and I played in every trivia game, saw several shows and spent plenty of time people watching at the dance club.
I really enjoyed the traditional dining as we made some great friends at our table to hang around with, and the food was good. As with any place, some nights were better than others, but there was always something on the menu I liked.
Just booked my next cruise on the same Ship Class and I think I'll be Loyal to Royal!