Sounds cool, the cave diving alone would make it worth the trip I'm sure, would love to do/be able to do that. I've been to Cancun once for a cousins wedding years back, and it really was plastic and full of fatties drinking on the beach all day was my impression. Funny story was we did a tour of the "Mayan ruins" one day, and my dad noticed that there were concrete forms along the foundations of these things. When he asked the tour guide how the Mayans would have managed that, the guy sheepishly admitted that they were actually originally 100 miles inland, but the Govt had just moved them closer to the resorts for tourism

Only other place I've been in Mexico is Zihuatenejo, which was a beautiful little sleepy fishing village near Acapulco on the south coast. If anyone remembers from the Shawshank redemption, it's where Andy tells Red to meet him at the very end of the movie. We used to go most summers when I was young, went back a couple of years ago and it now looks more like Cancun or something. The local hotels along the beach have all been converted into modern timeshares, there are even some American chain restaurants there now, quite sad really.