The Riviera Maya is a gorgeous area, with some of the most beautiful beaches I've seen anywhere. Playa is a city, and heavily oriented to tourism, but there is definitely a local population there, and there are a lot of shops and restaurants. Down the coast are a number of resorts, some all-inclusive and some not, and small communities like Puerto Aventuras and Akumal, ending up in Tulum. I like Tulum better than Playa -- it's smaller and somehow more intimate and friendly, and still has a lot of restaurant options. Tulum is also a better place to base yourself, if what you want to do is cenote diving. It's at least a 20 minute drive south from Playa to where the cenote tour sites start.
Cenote tours are big business down there. Do be careful in booking your diving -- make sure you are booking with someone who is APSA certified, or at least following the APSA rules. Those include a thorough pre-dive briefing, no more than four divers to a guide, everyone with lights, always with a guideline, and guide to be Full Cave and at least an OW DM, if not instructor, and to dive in cave gear. In addition, do NOT allow a guide to take you past the "Peligro" sign (or "Danger", if it's an NACD sign) under any circumstances. Guides have been known to do that, and there was a triple fatality down there this year as a result.
If you want recommendations for tour guides, do a quick search on "cenote" here -- there are many, many threads listing recommended guides.
I hope you do choose to come to this area. I really, really love it, and I never want to come home when my trips are over!
