My Wife and I stayed at the Iberostar about 6 months ago. My wife is a non-diver so we try to stay where there are things for her to do. While the Iberostar was nice, it was NOT as nice as other AI resorts we have stayed at in Mexico. I would second the thought that it is the 2nd or 3rd best on Cozumel. w/ the Grand being better. We actually had the "room" closest to the dock on the property. We were right next to the Dive Shop and right at the end of the Dock walkway so it was very convenient for me since I travel w/ my own gear. The shop let me use their tanks to rinse off my equipment, even when I dove with PapaHogs.
We had several complaints. Air conditioning did not work well. All restaurants except 1 are open air, so if you are wearing the proper attire (long pants) you can get quite warm. No real "bar" to sit in the evenings, just the lobby bar which is also open air. Fodd was good, service was adequate and staff was friendly
I Dove 2 night dives w/ DresselDivers (who is the Dive Shop for Iberostar) and was not impressed. The staff was friendly enough but dive locations are repetitive and they are a cattle boat operation. For the rest of my dives (6, 2-tank dives) I used PapaHogs because I have used them multiple times and I am comfortable with them. They will pick you up right from the Dock at the Iberostar and there are usually other divers staying there that dive w/ PH.
Hope this helps.