I dove cenotes twice so far, first Dos Ojos and about a month ago did Temple of Doom and Grand Cenote (which are very close to each other). As Bruce and Lynn have said, they are addictive! Playa is one of our favorite areas and I'll be sure to get into cenotes each time we head down! Dos Ojos was very cool a bit longer of dives than Temple of Doom and Grand Cenote. Temple of Doom was really cool for the haloclyne experience, Grand Cenote is just laid out really well and is a great spot to bring non-divers to experience snorkeling in cenotes.
Both of my trips have been set up by Jason w/ Fantasea Dive, we generally head over to Coz for a day of diving, a day or two of Playa reefs and a day in the cenotes w/ Playa Scuba. Have been guided by both Klaus and Luis and had wonderful trips both times! The diving is awesome and so is the little taco shop we stopped at on the way down - found a great shop just north of Tulum on the way home for tacos as well!