I've been twice on mid-sized boats, not those supersized monsters, although they look fun.
I thoroughly enjoyed it. I usually spent my time with a good book somewhere and found it very relaxing doing absolutely nothing. It was particularly nice on the day we docked in Mexico to stay on the boat while the majority of folks left.
Careful, it's easy to gain weight eating all those meals, snacks and desserts. But that's half the fun.
Sometimes though you see Americans at their worst. They pay bargain prices and expect to be treated like they are at Buckinham palace, having gourmet cooks, complaining about every little thing, being impatient, and eating like pigs at a trough.
Most of the workers are from other countries and they work like dogs. That bothered me. To see the same folks working the midnight buffet turn around and work breakfast, lunch and dinner.