The full-day marine reserve snorkeling/kayaking/hiking excursion is a PERFECT day. We have done snorkeling/full day boat outings with small group and private tour operators in Rhodes, Zanzibar, Belize, Santa Catalina, and Malta and this trip was by far the best we have ever done. The detailed planing, the quality, knowledge and friendliness of crew, (including how the helped each person have a great experience) and the quality of food, the boat, gear, etc (even the sustainability of the re-usable and sanitized daily metal water bottles were all top-notch). They limit the number of people to 14 and take you out with a crew of six to make sure everyone has a great experience. They plan the day to be different timing than other operators- so we were the only people snorkeling, the only people on the beach at lunch, the only people kayaking and the only people climbing the usually crowded steps to the emerald lagoon. They even have a crew member who is a really skilled iPhone photographer capturing your adventure on your phone!
We 100% and absolutely recommend this day trip as a “must do” in Koi Samui. Be sure to do it with this company (other guest at our hotel who went on similar trips with other operators had to deal with big crowds).