If you are truly seeking the real flavor of Mexico...Cozumel should be on your list.  It is quite simple to fly into and much smaller of an airport than Cancun.  It is also accessible by Ferry, from the beautiful sands of Playa del Carmen.  It only costs approximately $20 roundtrip to take the Ferry. 

Important note about the UltraMar Ferry Service: It's a 45 minute trip with "shipboard entertainment" consisting of three guys and drums - if you're not the type that likes it or can "tune it out" (mentally or with ear plugs), you may want to fly into Cozumel and save yourself this trip.

Once you get to the island, you can slow down and enjoy the simple things!  The town square is the gathering spot.  On Sundays, it is like date night and the locals dance and mix with tourists.  Bake sales can be found throughout with the best native goodies you'll ever find.  The square is surrounded by numerous shops and restaurants.  Something for everyone, by price or personal taste.  You are welcomed there, genuinely, by all.

Some of the best snorkeling/scuba can be done on many of the beaches.  The Playa Azul area is usually filled with beautiful fish and reefs. Convenient to restaurants, hotels and shops.  It really doesn't matter what area you chose, you are close to all the attractions, or you can choose to be as far away as you'd like!