I did the Aquacat in fall of 2004 and had a good experience. I agree with ghazgal on most points, although I can't imagine the boat running aground. Fortunately, we didn't experience that. Our two captains seemed very competent.
Not the best diving I've ever done, but very good diving and a variety of dives (walls, blue hole, drift, wreck).
I wasn't all that impressed with the divemasters though. One was kind of a jerk and the others seemed aloof. On a couple of dives, they gave poor directions to the reef, and they seemed more interested in taking photos of you that they later try to sell you than showing you sites.
The shark dive was interesting, but my absolute favorite dive was the dive after the shark dive. The boat stayed at the same site, so most of the others went on a shore excursion. With only a handful of us in the water, we saw a bunch of blacktip and carribean reef sharks in a more natural setting.
You should have a great time! While waiting to fly home, we ate a restaurant called the Poop Deck and enjoyed it. Food at and near Atlantis seemed outrageously expensive. Below are some underwater pictures from our trip.