My wife and I just returned from Florida and did the 3 tank trip with Looe Key. We did a wreck day so the first dive was on the Adolphus Busch.
The statement about cattle boat is fairly accurate - the do pack em on. Don't let that deter you though - the diving is worth it and they are a good operation.
The diving in the "finger" reefs is great if you are new to the sport. Max depth usually no more than 30 feet so each dive can be an hour of down time. Despite the shallow water, on the two reef dives we did we saw spotted morays, 2 giant green morays (5 - 6 ft), black tip reef shark, octopus, tons of fish - you get the idea. As far as critter watching goes, its great diving - and easy to navagate by yourself - so everyone goes off in thier own direction and it's very peaceful under the water. If and when we go back to the keys - that would be a definate repeat.