We did the Mayan Encounter through Alltournatives and had a wonderful time.
First we drove to the Mayan 'village' and toured through the jungle - we actually saw spider and howler monkeys up in the trees. We then did a zip line over a lake and a rapel down a small rock face - super fun. We then canoed over the lake (short distance) where we had a lunch prepared by the ladies in the village - typical Mexican fare. Make sure to take pencils, crayons, colouring books etc. for the kids in the village - no candy though as they don't have dental care.
We then headed out for Coba. Coba was great, lots to see. Its main pyramid is even bigger than Chichen Itza and the view from the top is incredible. We ended the day by swimming in a cenote. We didn't snorkel but I suppose if you brought your own gear along you could.
My only suggestion would be that you ask to be placed with a primarily English group. Out of 12 people on our tour my husband and I were the only ones who spoke English so the guide had to first talk in Italian to the majority of the group then turn to us and repeat everything in English.
Bernardo was our tour guide and he was fabulous - I would highly recommend this tour.
We paid $90 U.S. online through Alltournatives web site. Our tour operator offered the same tour but at a higher price. I would recommend booking online.