After a couple years of asking questions on this board, trying unsuccessfully to arrange trips from San Pedro, and doing research, I finally made it to Xcalak last week.
I have to say that, though my time there was brief, it was great! Great vibe, very laid back, makes me wonder if that's what A.C. was like 30 years back or more.
You don't go there for the nightclubs, bars or restaurants (aren't many of any of that). But if you like the simpler things (nature, the water, water activities) it's a great place to go.
We went and rented cabanas at Costa del Cocos, solar and wind-powered, and at night all we could see was the sky and hear were the waves. In the morning I went swimming off the pier out toward the reef, and never once did a motor boat pass me by. It was a very chill and laid-back experience.
The hotel/resort had numerous boats, diving, snorkeling and fishing equipment, as well as kayaks. The hotel lined up one of its employees to take us on a five-hour boat trip last Saturday. We boated down the river and Mayan cut separating Ambergris Caye from the Yucatan, snorkeled along coral heads, the reef and cenotes. Our hotel packed us lunch, water, soft drinks and beers in a cooler. Total cost? $50 pp for me and my friend.
Getting there, while not hard, isn't quick. We flew into Cancun, and Xcalak was five hours south. We might have been able to make it in one day, but to be safe spent the first night in Tulum.
There didn't appear to be much in the town proper, and most of the hotels and expat houses were north of town, off the grid, using a combination of wind, solar and generator energy.
If you're someone who likes the quieter type of vacation on Ambergris Caye, you might want to give it a try!