¡Hola Yvonne!,
Greetings from Cancun!
Hey, I agree with your review for Cancun.
I'd recommend you visiting Holbox island. It's a small fishing village which is not yet that touristicly developed. There are no paved streets, food's great and during the Summer, you can swim with the largest fish in the ocean: the whale-shark. There're also migrating bird's watchspots and the islanders are really nice people.
If you like colonial cities, I suggest Guanajuato, San Miguel de Allende, Zacatecas, Queretaro, San Luis Potosi, Morelia, Oaxaca and also Mexico City and Guadalajara.
I'm currently in Chiapas state visiting my parents and will be back to Cancun shortly.
If you'd like to contact me directly, look me up at the not so cold mail.
Hasta luego!...
Ruben :)