I love the Yucatan, so I guess I'll be the one to disagree here. I would not stay in Cancun but I loved a lot of places beyond it. I've been to Playa del Carmen, Tulum, went snorkeling around Xcaret, been to Chictzen Itza and Coba (Coba is one of the last temples you can actually climb), I've been to cenotes down there, and once drove on a dirt road to Punta Allen which is an incredible expanse of untouched beautiful beach, away from any development, though at the very tip by the lighthouse we stayed at a place with 4 big palapa huts centered around a restaurant run by a chef who vacations there from Paris every summer. Food was unbelievably good.
Our only bad experience was finding food on the unspoiled beach, but when we found a food shack, the unscrupulous proprietor tried to get us to eat some peppers that were off the richter scale. Luckily we recognized a scotch bonnet pepper when we saw it. That guy is going to kill somebody.
Friends tell me the city of Merida is a great place so that's the last remaining thing I want to do in the Yucatan.
I've also been to Cozumel but would not go out of my way to go there again.