The tour to Chichenitzen (sp) is very very worth it! Yes, it's long but it is grand. You can even climb the main temple if you want to, so yes, it's the real thing. The drive was about 1 1/2 hour each way, but we had a nice lecture about the site and the people on the way there and on the way back we boarded the bus, picked up a brown bag lunch and cold drink, lowered the window shades and napped on the way back.
I am not super duper into ruins but this was truly worthwhile.