I have been to Quintana Roo four times, mostly for the cavern/cave diving.
Cenote el Pit (maybe a mile behind Dos Ojos) is interesting, we saw a human mandible at 140'.
Another really unusual dive is Cenote Angelita - there is a layer of hydrogen sulfide between 90' and 100'. Below it is pitch black and it is very surreal above, like swimming through a layer of thick smoke.
I've never dove in Cenote Manati, just snorkeled there a lot (we usually stay at Blue Sky Hotel about 50 yards down the road). I've heard that you can dive into the cenote and exit in the ocean - I've seen where it leaves the cenote and where and where it dumps out in the ocean, both are very narrow and it is supposedly a very sketchy trip at best.
The craziest cenote I've been in was a sacrificial well at a spider monkey preserve near Coba. They lower you down with rappelling gear through a small crack in the Earth (known as the Earths's vagina) and you snorkel in a cenote filled with the skeletons of hundreds of Mayan sacrifice victims.
I've done a few others - Cenote Azul, Cenote Car Wash, Grand Cenote, and a couple others that I can't remember the names. If you plan to go back, 'Cenotes of the Riviara Maya' by Steve Gerrard is by far the best book on cenotes, although it is probably a bit out-of-date by now.
Some photos from the inside:
Warning sign in Dos Ojos:
Skull of a sacrifice victim:
My wife surfacing from El Pit:
Human mandible in El Pit:
