You’ll love it there. Like someone else said earlier, rent a jeep or better yet a crappy old convertible VW bug and go to the east side of the island for some great margaritas and fajitas at Mezcalito’s or Coconuts! It’s a great way to waste an afternoon! Casa Del Mar is far from the biggest or fanciest place there, but it’s clean and nice with good shore diving right accross the street. Before Hurricane Wilma messed it up, the shore diving for several blocks North and South of Casa Del Mar was really great. It was hurt quite a bit but has had three years to recover so it’s definitely still worth doing. If you haven’t already selected a dive operator, I would suggest Deep Blue or Blue XTSea. Both will give you personal service with smaller dive groups unlike the big cattle boat operators. There are plenty of other shops that are worth going with as well. As for ruins, rather than treking all the way to Chichen Itza, you might just check out Tulum or Coba. They are much closer to Playa. We took an early ferry accross, rented a car and went to both in one day and still had enough time to get wet in a cenote. Like others have said, you’ll have so much fun you’ll want to keep going back. I’m making trip number 7 this summer. Have a great trip!