This site is one of the popular tourist attractions in all of Mexico. It goes back more than 1500 years and the ruins are in very good condition. It was the crowded of all the sites that I have visited on both trips. Beginning in 2006, tourists are no longer allowed to climb the pyramid steps.
This site has more vendors selling stuff that I've seen in a long time. If patient enough, one can normally bargain them down by about half. This is not so much the case in the "official" site for vendors at a dedicated area at the entrance.
It is very accessible as it is located right off a very good highway connecting Merida and Cancun