The beach is very good, nice soft white sand and clear shallow water that's ideal for swimming, snorkeling, etc.
Overall Grand Turk is very much a worthwhile stop especially for those who enjoy the beach and watersports.
If you're into shopping, this is the place for you. There are countless shops selling electronics, jewellery, etc - all claiming great "tax and duty free savings". Hard to tell how great the bargains really are because no one displays a price on anything.
If you're into beaches there are a few good ones within a short (<10 minutes) and inexpensive (<$10) cab ride.
Excursions to nearby St. John are always an option and generally enjoyable.