We dove Media Luna this past spring ... clear waters, definitely warm and a few bubbly subsurface springs that you can play around in to pass the time. I´m not much for tight spaces so I can´t comment on any of the cavern entrances.
The dive shop near the highway on the way into the park area has several recovered artifacts on display in a back room - worth a visit if you speak with the owner.
Overnight camping at this site was very pleasant (we were just about 10 steps off the dive platform) and you can rent tanks & get air fills inside the park if you don´t want to drive back out to the main highway at the end of every tank. The dive shop inside the park didn´t offer as much in the way of gear, so if you are planning to rent or are missing anything, I´d recommend the first shop near the highway, but, otherwise, the park shop guys were great and hauled down our tanks (empty & full) at the times we requested to our campsite. Lots of ducks.
As always in central Mexico, bring your own rolls of toliet paper, etc. to use in the cabana house, as paper products weren´t provided during our stay. The path from the campsite areas to the cabana house weren´t lighted during our visit, so a standard flashlight comes in handy if you are there overnight. Weekend campers will find plenty to eat and drink at the tianguis (shops) in the center of the park, but be prepared to fix your own breakfast and dinner or to exit the park at those mealtimes, if you are there mid-week.