We are currently on the last leg of the World Cruise. It has been one of the most friendly cruises we have ever taken. Yes there are groups, they have been in close quarters for over 4 months now. They are still very friendly, it seems more like a big family party than individuals on a cruise. I have enjoyed the camaraderie.
I booked our shore excursions as soon as I could. There were 2 that had to be waitlisted, one cleared quickly and the other had openings the day of the tour. So, we got 100% first choice.
Dinner reservations were made as soon as possible. I got the days I wanted, but had to book an hour later for one, no big deal.
The ship is just fine. Yes, there are some things that could be redone, perhaps, but the overall condition is good, I can find nothing about which to complain. The toilets did have a flush problem one morning, but it was fixed and I just looked on this as a cruise experience!
Traveling with the World Cruise on the Mariner has been a super experience. If the itinerary is what you want, book it!