I haven't done any dives in the cenotes, but I've been snorkling in a couple of them
If you didn't done it... how you could compare? :O
And no, snorkeling in a Cenote isn't diving, it's quite the opposite: a very boring experience with not much to see and to do, since you will snorkeling only above the entrance so you see everything (aka nothing) in the first 30 seconds.
I understand that there could be ppl who doesn't like the Cenotes at all.. but try it, and you could change your mind.