I was at Xcaret about 5 years ago. I had a wonderful time. There is a wide asssortment of water activites, trails to explore, etc. Don't miss tubing through underground tunnels!!! The snorkeling is also great, or you can just sit on the beach and relax if that is what you want to do. They sometimes have a great show in the evening if you are still there.
Visit their website: www.xcaret.com
for more info.