The bus ride is long....but the buses are airconditioned and in good condition. The "sack" lunch was better than he expected (because of what he had heard).
He really enjoyed the ruins and felt it was worth the lengthy bus ride. Take something additional to drink with you. Make sure you use sun screen - at least before you leave.
Take along a camera...he took a disposable one (since I had our regular one in Merida)
and got some spectacular pictures. Wear comfortable walking shoes.
We spent a week in Playa De Carmen last year and took a bus to Chichen Itza one day. It was my favorite trip. The bus ride was long but there was so much to look at that we never got bored. We drove through many small villages and got to see how the people really live. Some things were pretty disturbing, like the starving dogs. But other things were very nice. Like old folks and kids playing in yards - no TV's or nursing homes! We had a very good tour guide who knew when to talk and when to shut up. We stopped twice on the way there to eat and potty and once on the way back. There was one of those scary step down toilets on the bus that I was grateful I didn't have to use. Hope this helps.