This was our second Disney cruise, first time on the Fantasy. Our first trip was on the much smaller Wonder, so we did have some initial concerns about the ship being too crowded. I can honestly say we never did feel boxed in. The only real time it felt claustrophobic was during the pirate deck party while waiting up top for the fireworks, and afterwords when we grabbed desert at Cabanas.
Overall, this was a great cruise and one that we would take again. We found our second trip on the Disney line to be much more pleasurable. Partly because our little guy was now potty trained, but primarily because we knew our way around and understood how to make the best of the entertainment, food options, shore excursions, and of course we knew not to overpack as we knew the laundry room was going to be our good friend.
I'll list some pros and cons and then some advice. Feel free to ask me any questions you might have, especially if this is your first trip.