Been a couple of times. It's not the best island in the world, but it's cleaner and a lot safer than most Caribbean destinations. It's gotten pretty darn americanized in recent years - a plus for some, a minus for others.
Rent a car one day and drive around the island. You really can't get lost, and there is some stuff to see in the backcountry.
Recommend Baby Beach for some cool, easy snorkeling and a good beach bar.
The italian place, La Trattoria El Faro Blanco, up by California Lighthouse is good and has some killer views back towards the high-rise area.
We took a cab to Superfoods (think slightly exotic Wal-Mart) a couple of times and stocked up on beer, wine and snacks. It's like $5 from the high-rise area, and it saved us a ton of cash on drinks at the hotel.
Just walking along the path that runs behind all of the hotels between the grounds and the beach is a great diversion. Lots of bars and quickie food places along the way.
Sneak into the Hyatt pool and use the waterslide.
Flying Fishbone is my other restaurant recommendation. It's way out of town down towards Baby Beach, but there are 4-5 tables actually in the ocean and it's a pretty cool experience. The beach there faces sunset, so it's damn romantic. As a bonus, it's a legit 3-4 star restaurant. Reservations imperative.