Our guide, Memo, was awesome. The tour itself was intense and awesome - the sights were incredible and Memo is a diver, so he had additional insights in the underground river. This place is like nowhere else I or my family had ever been, and we've been to a lot of places around the world (Hawaii, Colorado, Iceland). For that alone, it's worth going.
Food - breakfast and lunch - were excellent as was the service. The people genuinely seemed to like working there and they took good care of us.
Some feedback: The bikes are lousy. We had bad shifting and chains on the bikes. We peddled through some challenging terrain in the jungle and in caves, going up and downhill, over rocks and roots, and several other kinds of areas. You need a good bike and bike maintenance was really poor. That said, our guide traded me out his bike (which was slightly better) and took my bike, which was terrible.
Also, if you have friends or relatives with you who are skittish, be sure they know: bats, scorpions, spiders, and the notion of jaguars, pumas, and cougars could get them a little riled up. Forewarn them so they can opt out of this one if they'd like.
Same with fitness: if you're along with people who aren't fit or accustomed to riding bikes on tough terrain, they might want to pass. That said, they'd be missing out on an incredible sensory experience.
Also, be aware: it's 90 minutes to the site from the southern point of the Hotel Zone. Be patient with the ride and it'll pay off in what you see and experience.