Mexico can be brilliant. The beaches are gorgeous (especially around the "Mayan Rivera" in the Yucatan - perfect "white sugar" sand), there's Mayan ruins and the people can be really lovely.

A "must see" place in the area is Tulum, which combines the best of everything: beautiful white beach (with NO hotel developments because it's a park - just beach huts, and hotels in a nearby town), Mayan ruins on a cliff overlooking the beach, jungle, etc. It's completely different from Cancun, which has great hotels and bars but not much "Mexico."