The beaches themselves are beautiful, white sand, clear waters in general. Recommendation apart, not bring anything of value to the beaches as they are unsafe due to the number of people moving in the beaches.
During the day, very nice quiet place to walk around and enjoy the scenery. There are a wide variety of restaurants and bars to choose from on Ocean Drive. Lots of tourist shops around, also on Washington Avenue.
Point to note, you can rent bicycles to u$s 4 an hour at various points in South Beach. Segway can also be rented, is a nice experience if you never used one, about u$s 30 an hour.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.