As others have said, its essentially the kids clubs from the ship have gone to the island for the day, and works pretty much exactly the same. The counsellors come off the ship and onto the island. As long as your kids are registered for the clubs onboard and have their bands they are good to go (although you can register at Scuttles Cove if you need to).
Its pretty much a giant sandbox with a wet deck, volley ball and soccer nets, loads of toys, a whale dig, craft options; they have a beach party, play capture the flag, relays, water fights, bubbles, sandcastle building... like the ship theres a full day of activities...
The majority of the kids really like it, but if your kids really like the clubs onboard because of the screens, lights, music, characters, busyness, iPads, movies, constant/big options of entertainment, then Scuttles Cove might seem like a bit of a let down...there's not really any electricity haha! There's constant activities like on the ship and kids aren't made to do anything, but probably a bit more on the chilled/calmer side. If they need space to run around and just be outside they tend to enjoy it.
The one thing that is different to the ship though, is that any kids that are in care for lunch time, get taken to lunch even if they dont want to eat (there isn't the option to go and play like onboard), they obviously don't get made to eat but they do have to sit there while the other kids do if they choose not to, and if you want to pick up while lunch is navigated, then you'll get directed to Pops Props as thats where the kids are.