As their private island, Great Stirrup Cay is owned by NCL and therefore they are the only game in town - or on the island. Roatan is a different story and there will be lots of taxis and tours on the pier that will go to Tabayana Beach.
Great Stirrup Cay is a very rustic place, mostly just sand and scrub brush with maybe 200 acres above water. All the food and drink comes from the ship - they will have a barbecue and some bars up and running. It is mostly a beach party although there are some things you can sign up to do - and pay for - through the ship.
Well, I loved staying there. In a week I had three or four days with ship calls, and the other days were all mine! GSC in inhabited with 4 NCL divers and 1 norwegian engineer (governor ) It's amazing to have the beach all to myself.