I stayed at the Iberostar in Cozumel for 12 days last April/May. Hubby and I (<50 dives) plus another couple (<200 dives). We had a great experience and would stay there again when we return to Cozumel. Although we are novice, we have done some very popular dives -- Roatan, Belize, St Lucia, Puerto Rico, St Thomas... Cozumel was amazing, just for the awe the formations of coral and all the swim-throughs. Probably my favorite spot so far!
Dressel divers were good. Nitrox is free, so we obtained our nitrox certification there and used nitrox throughout our stay. They have three boats, which were always full. We found that we needed to reserve our spots for the entire week as soon as we arrived. However, there were sufficient DMs so that there were never more than 6 - 7 in our group. Three boat dives each day with a schedule of dive sites posted -- helpful in planning our dive. We purchased a large packsge of dives which they allowed us to split between four divers, plus we pre-paid our dives and saved addition $ that way. I think it averaged out to be about $25 per tank -- and that was nitrox! We felt we got a great deal, plus the resort itself was a package thru Apple Vacations and ended up being quite affordable. The dive sites were all a very short ride by boat; so close, in fact, that we spent our surface intervals back at the resort.
The resort was very nice, btw: not luxury, but certainly on the higher end of what is available in Cozumel, perhaps? Not close to town, but we never felt the need to leav the resort! On the beach; nice pool; decent food (three specialty restaurants included, but require reservations), all drinks included (frozen pina colada and strawberry marguerita machine whirring continuously and can be enjoyed without alcohol), nightly entertainment (a little lame and cheesy, but we are early to bed anyway.) We did enjoy the beach party one night, but never stayed up late enough to see the nightclub. Daytime activities and an entertainment staff to keep things lively. Peacocks roam the resort, but the flock of pink flamingoes stays in the lagoon and the parrot keeps to the lobby.
I must caution, however, that it IS Mexico and one can become very ill -- I spent the last 4 days unable to keep food in my body and was hospitalized for 4 days as soon as I returned home. The resort uses purified water; we even used bottled water to brush our teeth and no one else got sick, so our best guess is the lettuce and other uncooked salad veggies were probably washed in local water -- I was the only one that ate salad. So just use caution and don't eat the salad. Having said all that, it was a very enjoyable vacation and I would recommend it.