We just got back from Cancun last night and had a wonderful time. My son and I had just gotten certified before we left and my other son and wife do not yet scuba, so we, too, were interested in dives for beginners that snorkelers could enjoy as well.
We dove both the Cenotes and Manchones (near Isla Mujeres) and everyone seemed to enjoy both dives immensely. We used Scuba Cancun and they did an excellent job working to meet our requirements.
On our first dive, my son and I had a Divemaster all to ourselves, which was really awesome. He helped us get properly buoyant and was very good at finding interesting aquatic life. The rest of the boat were all snorkeling and they too reported seeing a lot of fish (though they missed the turtle!)
On our second dive to Manchones, there were three other beginner divers who were doing their OWC dives. This wasn't as good since we had to occasionally wait around for them to do some of their requirements, but I really didn't mind too much as there was always plenty to look at on the reefs. We much preferred this over going out with a bunch of more experienced divers and/or being lost in the shuffle of a larger group.
As for the conditions, in general, the currents were fairly strong, though most of the diving outfits seem to use drift diving, where you just drift along with the current and then the boat comes and picks you up wherever you surface. The seas were calm--no one seemed to have any problems whatsoever with the swells or choppiness.