Yes, these countries are beautiful but totally different ports than a typical Southern or Western Caribbean itinerary. Beaches are very limited, so planning a tour is a must. If you have not obtained a copy, get a copy of your ship's tours directly from the Cruise line. Belize is known for its barrier reef. You will tender here. The ecology in these countries is very protected. There are some Mayan ruins, Cave tubing, River Wallace, Baboon Sanctuary, Belize Zoo, etc. Check out a review on cruisecritics from Wysteria who just returned from this itinerary. She is an objective writer. Do your research. Limon boasts of the Aerial Tram through the RainForest and Tortugeua Canal tour. Colon of course you can take any number of canal tours even sailing on a ferry in the canal. Shopping is very limited, so spend your money on an excursion to remember your cruise by. These ports are being just developed. People are friendly, but be aware of your surroundings, too.
Bon Voyage