Tiny wavelets on West, North, and Northeast blows. Perfectly glassy flat on East and Southeast days. Saltwater lagoon so big you can't see the other side. Kite out for 2 km, fall off, and stand up to your waist. Flamingos, rays, horseshoe crabs, maybe some crocs but we´ve never seen any.
Warm enough to be just in shorts and a rash guard except during December to February when the North front is first hitting at which point you might want a shorty.
Season is pretty much November to end of April with best months December to February. Usually best in the mornings, at least 5 days a week in the before mentioned months, all directions are kiteable because offshore winds present no problems due to shallowness of lagoon. Have a good kiteleash cause a lost kite is a gone kite up here. Flattest directions are East and Southeast.
From Cancun drive North towards "Punta Sam" and the farthest North ferry landing that goes to Isla Mujeres. Ask for directions to the beginning of the new hotel development called "Playa Mujeres" and then convince the guards to let you through (not too hard usually) and drive 20 minutes of hardpack (probably be paved by the time you get here) until you have the ocean on one side of you and the lagoon on the other!