I went to Cancun years ago and stayed at the Club Med, which has since been remodeled. I was pleasantly surprised w/ the resort.

I would second the recommendations on Coba and Tulum. We visited the pyramids and I was awed. It was years ago when they actually let you climb up. My friend went in December and apparently you can't do that anymore, which in hindsight, is probably better.

The past 2 years we've been going to Ixtapa but the Cancun area/peninsula has more to offer by far.