I am a well-travelled scuba enthusiast & have been to Cozumel MANY MANY times, it's one of my favorites, but be careful here. My trip was paid well in advance and although I had a confirmed voucher for the room, when I arrived at the resort I was told there was no room for me, they were sold out, completely booked, and that "I would have to find someone to bunk with".
I recognized the problem, I am a single female tourist and they want double-occupancy for financial reasons. Knowing I was meeting a group of other divers there I was told to ask around that group and see if I could bunk with them. I refused, and they said I have no room. It took a good 20-30 minutes of fighting, insisting, and then actually setting up camp in the foyer before they amazingly found a room for me. This was even worse! My room was infested with ants, ants everywere, and a heavy stench of a perfumy substance mixed with the powerful stench of mildew. It didn't help that the A/C was poor and loud.
The grounds are nice, the food on most nights was edible or at least you could forrage for something, and the dive shop was GREAT - that was the very best part of the stay. If you're not a scuba diver, stay out of this place, I doubt you will enjoy yourself at all. There is nothing worth shore diving or worth a snorkel here either. You are far from the square and there are much better choices of resorts for non-divers. If you dive, you might be OK with the stinky rooms, I have actually seen worse.
Of the MANY places I've stayed, I think I enjoyed a place called Iberostar the best - but I didn't dive with them while I was there, so I can only vouch for the food and lodging, which was terrific for Mexico standards, although they had only been open for 8 months when I was there. I hope it's still good. Be careful folks.