When we go to Cozumel, we decided on doing Mr. Sanchos Beach Club which seems to be very well reviewed on Trip Adviser. It's an all inclusive place that includes food and drinks and a number of other activities are available for more money. It's down the road a bit from the Mayan Cacao company so I got us tickets for that as well. From what I've been able to dig up, the pictures you see of the ruins on line are pretty much it, a little underwhelming. I figure for a self planned excursion, it's not too risky since you can come and go when you want, it's not that far from the cruise piers and taxi rates are fixed. It would be missing some of the cultural aspects that those other tours include, but those are a bit contrived anyhow. Worth taking a look at, at least!