DON'T DO IT!! At least not through the tour operator that Sandals uses ("Spirit of Carnival"). My husband and I did this tour earlier this month. You will get up at the first crack of dawn and rush through breakfast just to be bussed to an overcrowded "party boat" which will take you to Soufriere after sitting on the boat for 2 hours doing NOTHING.
When you finally get to the gardens, they are GORGEOUS! However, the tour was EXTREMELY rushed - maybe only an hour or so - barely time to ask questions or take pictures. We were then taken to the cafe for lunch, at least the food was good and the other people on our tour were cool. Then after being bussed back to the boat, we waited another 2 hours doing NOTHING while waiting for the other tours to finish. They then take you to a spot to snorkel. The captain obviously knows NOTHING of maritime law - he pulled up next to a boat with a "diver down" flag raised, with engines in full bore. He could have seriously injured the scuba divers that were in the middle of their dive. By the time you are able to push through the throngs of people to snorkel - it is way too crowded so no room to navigate around. Then back to the "party boat" where they serve you pre-made "cocktails" with the ice already half-melted. The grand finale was them stopping by another boat on the way back to the dock, to throw them the box of snorkeling gear we all just used, which had not been cleaned or sanitized. Each boat is supposed to have their own snorkeling gear (according to Sandals, anyway).
We complained to Sandals but they refused to refund our money ($198 down the drain for 2 people), and since it was at the end of our stay, we weren't offered a credit towards another tour. I strongly suggest seeking out Charlie on the resort beach - several people raved about his tours and they are MUCH cheaper.
Edited: 2:55 pm, January 14, 2013