The gateway to Yucatan, provided you are not ruin-fatigued. We only got to Chitzen Itza due to already having been to 3-4 Ruins by then. The tours were also highly marked up compared to other cities in Chiapas/Oaxaca.
We stayed in a run down, colonial hostal at the Zocalo (Hostal Zocalo) which was nice and central but everything creaked. The receptionists also had a few strange friends who looked in need of a shave and a bath that came over to hang out. Mosquitoes will chance any opportunity so apply the necessary. Most of the fruit at the market were in dire states due to the heat. Although sweltering and too crowded for my liking by day, the city was very vibrant at sundown and had events every single night. We managed to catch a Mayan ball game and a spectacular traditional music and dance performance.
Since tours were expensive and none combined Chitzen Itza with Ik’kil cenote (just 5km from each other) we took the first ADO bus there and the 5pm one back. There is a local bus half-hourly between the two attractions but not many taxis so be sure to plan ample time to make your way back to the ADO bus station at Chitzen Itza. Another alternative is to store luggage at Chitzen Itza, and take the onward bus to Tulum/Cancun, which is what we feel we should have done.
Chitzen Itza was considerably less crowded at 8.30am when we arrived, and the best decision we made was to go straight to Ik’kil at about 11am before lunch. That gave us a peaceful swim before the post lunch tour groups thundered in. The post lunch photo below has the crowds cropped out, and the magical beam of light streaming straight down at noon had shifted to a sideways radiation by 3pm. (PM me if you really want the picture of the crowds). I regret not having brought my camera down when we first arrived.
In Merida there are a handful of museums to engage in, but mostly it is best for a centralized Yucatan exploring place to spend the evenings.