No no no, do check it out if you can. It's really quite spectacular. That whole peninsula is former reef limestone ..it's like a big giant porous piece of dried out live rock (with grass and trees and stuff growing on top). Anywhere you see a puddle, that puddle is probably connected underground to every other puddle, and probably the ocean. I remember seeing a pond, or what I thought was a pond, on the resort grounds, only a couple feet in diameter in size (ie., tiny) and then noticed that it was at least 6 or 7 feet deep, and had reef fish swimming in it. They got there themselves through some underground maze.
I think the cenote is usually done in conjunction with another day trip. I can't remember if it was Tulum or Chichen Itza. Although neither are rather reefy, they reek of history and you can really feel a buzz (well, if you're into history and old things and stuff). You HAVE to check these out in my opinion, you won't regret it.
The one and only complaint I had about Barcelo Maya is that there was a 1/2 hour limit per day with the catamarans. Being that I pretend to be a sailor in my other hobby, this was sort of disappointing to me because 1/2 hour of crashing about in those waves was over in a blink of an eye. They also had kayaks and windsurfers though with unlimited usage, but windsurfing for me was impossible in those waves, I'm not a strong windsurfer so it was an exercise in futility. I'd just get upright and then knocked off balance instantly.
Maybe they have more than 2 beach cats now. For the size of resort, having only 2 and rationing them out like that was rather silly.