I love Playa del Carmen Mexico - just got back!
We honeymooned there years ago & keep going back.
It is more laid back than Cancun - I am not into the spring break crowd anymore - I'm 36. I much prefer PDC.
If you're looking for an all inclusive I highly recommend the
Royal Playa Del Carmen. It is fabulous my favorite of all the AIs we've been to - it is also only steps away from downtown Playa del Carmen so you can walk into town for additional nightlife, shopping, cozumel ferry, and dining. It's the best of both worlds.
We LOVE all inclusive but hate feeling isolated. This takes care of that - not isolated at all yet still get the warm fuzzy AI resort feel. This is an adults only resort. You can check it out here:
http://www.realresorts.com.mx/The_Royal_Playa_Carmen/