Playa del Carmen
Playa del Carmen has really grown up! The daytime has nice atmosphere for shopping and lunch, good for families, and beautiful beaches. When the sun goes down, it has a whole different character with fun restaurants. Late at night, the nightlife really heats up. There is no parking to be found, so best to take a taxi.
You can take a ferry from Playa del Carmen over to Cozumel for the day, but there is great diving very near Playa del Carmen, including the Cenotes.
Akumal is another 30 minutes south of Playa del Carmen. Great snorkeling, nice beaches, and fun beach restaurants.
Sandos Playacar Resort
Sandos was a fun all-inclusive very near Playa del Carmen. There were multiple swimming pools, free water sports (sailing/catamarans, sea kayaks, and boogie boards), fun activities (water aerobics, dance lessons), and evening entertainment. The beach was beautiful and goes on forever. There is a Scuba shop on the premises.