I did it a few years ago. It's ... fine. The boat was well-run, and when I went there were only three of us diving on the boat so it felt like a private excursion, which was wonderful. The guide was really helpful for finding some of the more interesting spots along the way. We did two stops, one of which was a pretty active reef, and the other was a bowl-like area that was pretty empty. We saw turtles and a pretty decent variety of fish, but overall it's one of the least active places I've dived (it might have just been a slow day). Both areas were shallow enough that you could have had a fairly similar experience on a snorkeling expedition. (Personally I find a dive much more relaxing than snorkeling and consequently worth the extra hassle, but my wife would strongly disagree).
I'd do it again, but mainly because there isn't much else worth doing in Nassau--there's only so much rum I can drink.