We went on this trip in 2010 and it was fantastic, great coral, sea turtles on a quiet relaxing island. 2012 was an experience I would rather forget.
The setup is coaches pick you up in Cairns and take you 45 minutes south (or you can drive and leave your car near the wharf). Then a short trip down the river (if you are lucky you may see a croc.) and then 20 minutes or so to the island. You are then transported to the island by the glass bottom boat etc. On the island there are some tables under traps.
You can have glass bottom boat rides, snorkelling or island tours, by friendly staff. We went snorkelling by our self. Then lunch consisting of prawns, chicken salads etc. All of which were quite good.
Now where does it all go wrong? First when the tides are not right you only get a few hours (compare to 5 hours plus on 1st trip)on the island, as the boat cannot get over the sand bar. Then the glass bottom boat engines play up so we cannot get back to the main boat. Then the main boat cannot get into the river due to the tide. 5 hours plus waiting on the boat for the tide. Back to the hotel at 9:30pm, at least they could have provide a meal? Yes a free drink each on the boar, but no food available. We were told we would be contacted by the manager the next day, this did not occur. I rang several times and was told someone would ring back, this never happened.
Other downsides there were insufficient snorkelling gear for everyone and what was there was mouldy. The coral was still recovering from cyclone.