Jim,
The beaches are lovely in their own way. It's not the wide sand expanses of the Gulf Coast, it's not the vigorous Atlantic, it's not the cliffs of the Pacific.
The beaches are narrow, lined with gorgeous palms which whisper in the Caribbean breeze. The water is amazingly clear and relatively quiet on the reef. The marine life is stunning. There are fabulous snorkel trips (I don't dive either) where you'll see vibrantly colored fish, southern stingrays and nurse sharks. Close to shore, many beaches have seagrass which isn't the best for swimming, but is an important "nursery" for the sea creatures. There are places to swim around various piers and in front of Banana Beach Hotel (and others).
There's plenty of nightlife. Even better, I love to visit with locals and tourists alike while walking the beach, lounging on the beach, or tooling around in town during the day. You can rent a golf cart or a bike to tour the island. There is a nice variety of restaurants.
This will be my third trip to AC and I haven't seen everything yet. Nowhere near tired of the place!!
When do you arrive?