We came over to Isla Mujeres on a catamaran tour, so only had a few hours to spend exploring the island. We rented a golf cart and after checking out the turtle farm, made it to this place--Garrafon de Castilla--for some snorkeling. The snorkeling was excellent, and the cost was low enough that we didn't feel bad about the fact that we weren't going to be able to spend very much time there. We rented a locker for our valuables, just to be safe, and had no issues whatsoever. There were plenty of other people there, but I wouldn't call the beach crowded. One thing to note was that there were a couple of women on the beach who chose to go topless. This was not a problem for us, and I don't know how common or uncommon the practice might be at this location, but if seeing a topless woman on the beach would be a problem for you or your family you may want to research this a little more.
We thought about eating at the restaurant, but it was crowded enough that we couldn't get a table and we feared that we might miss our boat if we waited and ordered and then didn't get our food very quickly, so we wound up not actually eating there. The prices, though, seemed reasonable.
I'd definitely recommend this place if you're looking for an inexpensive location to spend some time on the beach or to do a little snorkeling on Isla Mujeres.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.