I worked in Puerto Rico a number of years ago and have spent quite a bit of time there, so we weren't that eager for this port of call.
Positives - the port was clean, there was a nice walkway along the port, we were able to walk to the Fort quickly and easily. The Fort is beautiful and an inexpensive, enjoyable experience.
Negatives - the path to the fort is not well marked. Our 4PM arrival time didn't give a lot of family-friendly shore excursion options to choose from.
The boat ride to St. John was great. The Captain narrated the ride over and shared some interesting information about St. Thomas on the way over. The walking tour was short and there wasn't that much to see. There wasn't really enough time left to go to the beach or do anything but walk around the shops.
I am amazed at how much Royal Caribbean has improved Labadee since my first visit there in 1990.
We rented a cabana in the Barefoot Beach Club with friends. We were in and out so there was plenty of room for the five of us, but if you plan to be in the cabana all day three is a more comfortable number. The cabana was well worth the price, we enjoyed the shady area and the quieter beach experience. The upgraded buffet was okay - the major upgrade I saw was that they served seviche and there wasn't a long line up.
The shopping at Labadee is terrific in the Artisan's Market. Prices are marked and it is a hassle free experience with some wonderful unique items. Be sure to bring cash or your credit card! There are a lot of interesting items out in the Artisan's Village, but it is kind of a free for all and the vendors can be a bit pushy.