Just got back from the 7 day Disney Fantasy Western Caribbean cruise and I'll admit I went in skeptical as it was my first cruise and I'm not a big Disney fan even though I have girls aged 7 and 10. But I got off the boat completely impressed and eager to do it again in a couple of years. Since I gained so much reading reviews on this site prior to mine I'm just going to focus on paying forward some additional tips for those who are going soon. Note that due to high waves our cruise did not get to stop in Grand Cayman which was a disappointment but what can you do? Costa Maya is frankly, a dump and I love Mexico. Best option is to take a cab to Muhahual's beaches. Do not be conned by the gauntlet of folks telling you that you'll be better off to buy an inclusive package. We got suckered into Senor Frogs for $15/pp but we could have cabbed it there for free and hung out and ordered food/drinks there. And it is the place I'd recommend and then you can walk the malecon a bit. In Cozumel we knew we wanted to cab it to Chankanaab Park and we are glad we avoided the gauntlet of vendors and did it. $13 cab ride, $20 admission but well worth it. Spent a great day there snorkeling, walking, swimming, sun tanning. Kids had fun also playing in the hammocks while the adults had more fun at the tequila tasting (ole!). Last stop was Castaway Cay which was phenomenal but I regret that I bought the Getaway package as we already had our own snorkel equipment. My suggestion would be to buy just one or two packages and share it. The snorkeling is only OK there, its fun to swim around there. Biking is fun and definitely if you like to run do the 5k race they set up, it was a great way to see the island before anyone else.
We had room 5548 with the oversized verandah and I would book it again in a heartbeat. Having the bigger deck (plus we connected to 5550 where my sister was) allowed us to open up the deck between the two so we could relax and avoid the masses up on deck 11 where it really does get crazy. The "pools" are essentially a cool place to stand, kids liked it for a bit but it wasn't their favorite place. The only negative I could find is that the Oceaneer Clubs have too wide a range of ages (3-11). My girls being on the upper end found it rather boring, nothing against the great team there, its just there is a disproportion of kids in the lower age range and the activities are geared more towards them. I think they'll enjoy that part more in 2 years when they can do the 11-14 activities in the other rooms which looked like a lot of fun, the tweens were having a great time on the boat.
Bring magnets to decorate your door so your kids know which one is yours. Bring wipes to clean off stuff and a little thing of dish soap to wash out reusable water bottles to take on the shore excursions. We brought a good selection of alcohol which helped ease the on board bar tab, but a good option is to buy the drink in the souvenier cup and then you can get it re-filled with the drink of the day for half price the rest of the trip and those were GOOOOD! The gym is very crowded from 6-9 a.m. so if you are an eager workout fiend plan to get up early or sleep in late.