Adventures Mexico contracted with Turistran Merida for the tour operation, so the review is really for them. Chichen Itza day trip from Merida, as described*, was a good long day. About 35 of us total on the trip, 65/35% Spanish-speaking vs English-speaking, so there were 2 guides on board + the driver. Very friendly, professional staff and they were obviously well-versed in the routine. Picked up at hotel ~9:30, and returned at 7pm - note, that's an hour later than listed, but my experience with these types of tours is that's common... Comfortable, air-conditioned bus for the 1.5hr ride to and back again. On site at CI, you get a very quick overview guided tour for about an hour, and then you have n hour on your own. That timing seemed rushed - people on their own may spend 3hrs at the site- but the two of us did have time to see everything (I think). The guides definitely did seem consistently on guard for timing. Next stop, 40 minutes at the nearby Ik Kil cenote which is neat to see, and an opportunity to dip in a fresh pool after a hot day. The buffet lunch at Hacienda XaRe was last - by the time you do it at 3pm, you're so hungry that you don't mind the letdown of it - it's a massive buffet cafeteria for tons of bus groups all day long, and food not so great, and a bit of a clamorous mess hall. But again, you're so hungry... Overall, a standard day trip run by competent, friendly staff. Sure, CI is a new 'wonder of the world', so worth seeing. (For Mayan buffs, I think Uxmal is better, but smaller).
*Note that on Adventures Mexico website, on this day trip page, it does say (at the time of booking a couple months ago and still today) that "we include...entrance fee..." on the top caption of the title description. That is not correct, and the entrance fee (to CI and to Ik Kil for that matter) is correctly listed as not included details lower on the page, and on the voucher you receive. CI entrance is only ~$12USD, so no big deal, but a slight confusion on what to expect / hope for. (p.s. to Adventures Mexico...would be good to include it). Also, note that CI is very popular and very hot, with limited shade. Sundays, Mexican nationals get in free, so it's even more crowded and hectic - pick a different day if you can, unless you're a Mexican tourist and want t take advantage of the Sunday!
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.