Akumal is definately layed back, so relaxing should not be a problem. In fact, I think you will find a slightly older crowd there.
There are several small shops in the Akumal area that are within walking distance of ABR.
Although snorkling is excercise, I find that relaxing and that is one of the major attractions in Akumal. Close-in reef to the bay and lot's of turtles and sealife to see there. No snorkel tour needed. Just swim out directly from the beach.
It's all about location there. ABR is a older resort and because of that is layed out in a more horizontal fashion, so most all rooms are are considered oceanview. Go for a room in section 5 or 6 is my recommendation. Section 5 looks out over the pool towards the beach and is a more central location. Section 6 is newer and away from pool area and probably quieter, however further out on the south side of the property. Three star hotel, but good service and vibe there.