We went a couple years back for my brother-in-law's wedding. It was awesome! The resort was nice, all inclusive, and had just about everything you would need when there. I can't remember the resort name, but it was in Riviera Maya. The have all kinds of tourist places off the resort as well. As others have suggested, I would highly recommend checking out the Mayan ruins and the cenotes that are close by to there. If you want to hit up Cozumel, its a 45 min taxi ride to Cancun and a 30-40 min ferry ride to the island. We took a catamaran ride and did snorkeling when we were down there, It was a ton of fun.
The resort we stayed at had a swim up bar in the main pool, and would give out snacks all day long (pastries and such). We would grab a few of the churro rolls they had and take them to the beach. If you wade out about waste deep there would be all kinds of fish that would come up and eat right out of your hand. Water was super clear too even with a storm that came through when we were there.