Anne,
My wife, kids and I went to Playacar or Playa del Carmen about 6 years ago. I'm sure it has changed but I found it to be a pleasant spot. Slow pace of life, great scuba diving, nice beach. Negatives were some kind of jellyfish that stung and came in and out. There were warnings on days not to swim in the ocean. Also, the reef is fairly close to shore near the southern end where we were, so limitted ability to swim out. Didn't bother me.
We took a day trip to Chichenizta (sp?) and it was fabulous. Kids still remember that part of the trip! lol.
Cheers,
BearBath