It is fun when u have a lot of friends to go together, can play games on the beach, enjoy the free sunshine and breeze, and the most important thing is, it's much much cheaper than Santosa or East/West Coast Park to have one whole day's fun.
One more suggestion is, bring ur lunch with u. The food shops are only located at the entrance of the island. U don't want to ride all the way back to get food, and ride again to the beach right?