Its a pretty cool place. Try all of the restaurants. I would highly recommend being at the restaurants at least 15-30 minutes before they open for dinner. It will save you a long wait time. The Italian restaurant at their golf resort next door is awesome (The reason could have been the 10-12 Jack and Cokes I had). The buffets are actually pretty amazing.
If you like historical stuff, there are some Mayan Ruins a couple hours away. Tulum is Mayan ruins and happens to have one of the top 5 beaches in the world out back. The view is worth the two hour bus ride.
Theres also the typical entertainment. Para sailing (sp) and Jet skis. Game rooms and club type dancing. If you want to dominate some European kids at ping pong, theres that opportunity too.
I will say this, the beach sucks at Moon Palace. IDK what it is but there is just debris all along their coast. If you or your spouse/significant other like the beach, take advantage of a shuttle to one of their other resorts.
Drink a lot and try the guacamole. If your rum bottle in the room runs out... have them fill it up.