We just returned from a stop at Belize. It is a tender port, so do allow for the up to 5 mile Belize tender ride. Travel to anywhere does take time. The port Tourist village is nice with many small shops. Don't miss a stop at the Pharmacy if you need anything for less compared to USA prices (no perscription needed). There are no beaches nearby to the port. Water taxi schedules can be obtained on line to Ambergis Caye which is a nice snorkeling or sunbathing site but don't miss the taxi! We took a private tour with Reggie Tapp and did Cave tubing @ $65pp vs. $85 from the ship but ours did not include lunch. Reggie is an excellent guide with a nice crew of family and friends that assist him. He did recently refurbish an airconditioned small school bus. He guarantees that he will get you back in time for the tender or will tender you himself. This is his only business so he knows what he has to do to keep everyone happy. He often tries to stop for lunch if time allows. His tour encounters at least one more cave and a longer hike at Jaguar Paw but it is the same site that the cruise ship will use. If this adventure is too strenuous for you or you have young children along, he will help you plan a tour just for you. The other often recommend ship tour would be the Altun Ha and River Wallace tour. These ancient Mayan ruins are nothing to be compared to Tulum or Chitcenitza, put if you have never seen them, this could be interesting.
There was a great story recently on this board about the new Costa Maya port.