Wife and I just came off the ship yesterday after the Seven Day Mexican Riviera itinerary. We've been on two recent Carnival trips and this was our first Princess Cruise.
EMBARKATION - Very Smooth. We arrived around 12:30 or so and were on the ship in about 30 minutes.
CABIN - We selected a balcony cabin and were told that our six year would have a "Murphy bed." We found out that for our cabin this meant a bunk bed which was stowed in the ceiling during the day. Our son was a little apprehensive about it, but learned to love his bunk bed. Cabin size seemed a little smaller than Carnival. Our balcony was approximately 3ft by 8 ft or so with 2 chairs and a small table. On the Aloha deck, the balcony was covered, unlike some of the other cabins on the lower level. It would be very difficult for someone to peer into our balcony area. Bathroom seemed comparable to Carnival. We asked for robes and they arrived within a few hours on the first day.
Adequate storage space - especially since your luggage can go under the bed. Balcony was fine for 2+ child, but would be cramped otherwise. Cabin was very close to elevators, but not too noisy.