I have never personally been to Mexico (I thought I was the only one!), but I have a group of friends who swear by Huatulco and go every year.
This.
Been there, loved it.
There is a night life, but not nearly as chaotic as Cancun or any of these "spring break" locations.
It isn't as commercialized as the more well known towns.
There are a couple of new resorts there, but I don't know their rating or the reviews, as I have stayed in a condo owned by family.
I found it to be a very good "intro" to mexico, as there is a high population of Canadian Expats there. Several of the businesses are owned by canadians that have moved there.
But there is definitely still that native mexican culture there, so you don't have to worry about missing out on the experience.