We had booked this trip direct before we left the UK and were very impressed with the organisation, down to dealing with our change of hotel (and therefore our pick-up point and time).
The park has something for everyone, from snorkelling to swimming the underground river and from walking on the sea bed to swimming with dolphins.
If you decide to visit, make sure you leave enough time to see the show at 7pm (some tours leave at 5:30pm), and pay the extra for dinner at the show when you book, as it is well worth it--you get the best seats.
For a better idea of the park, visit the website at www.xcaret.com
, where you can also book online.