We have a Merrytime Fantasy cruise coming up this December and are opting out of the character breakfast, because we didn't enjoy it much last time we were on the Fantasy. We don't care for the Disney Junior characters, the breakfast itself was sub-par, and they stuck us at a table with another family who ignored me when I said hello. They moved us to our own table upon my request, but it still wasn't a great experience, with the very limited breakfast optons & the rushed nature of it. They made us stay at our seats when the characters came by- no standing up to get a good pic with Mickey (the only non-Junior character who was there). It was very unlike the interaction we were used to from character breakfasts at WDW.
On the Wonder in Alaska, we had a much better experience. We asked for our own table upon arrival & were given one, it was the Fab Five instead of Disney Junior characters, and the breakfast itself was actually good.
So we'd do it again on the Wonder in Alaska, but not on the Fantasy.