We went to Chankanaab for the dolphin encounter experience. Finding a taxi at thenpier was quite and adventure as it was rush hour and they squeesed us in a van with several other people. Negotiate the rate in advance: at the taxi stand I had seen that the rate from Punta Langosta to Cankanaab was 11 USD up to 4 people, yet the driver asked me 20 (but when I said 11, he immediatley accepted!).
Chankanaab is a lovely place. You find wooden deckchairs, sunumbrellas, hammocks, white sand and palm trees plus a spectacular reef just from the shore, so you can easily snorkel even with kids.
The dolphin experience was nice, yet a bit too commercialised.