Something like 80% of the reef immediately off Akumal has been classified as "dead" in the last 3-5 yrs. Very sad. I've been going to Akumal for many years and love it, but I've watched the reefs go from pretty good by Caribbean standards to having dives where seeing a live seafan, 2 eels and a few lobster and a handful of fish was considered good. The reef structure/topography around Akumal is gorgeous... but sadly in recent years not so thriving anymore. While I can make any dive a good dive, honestly, if you're someone who wants to roll in, drop down and be wowed then Akumal won't make you happy. If you want to see turtles, lobster and eel, or you have very low expectations and diving is not the main focus of the trip, go for it.
One nice thing about Akumal diving, especially in recent years, is that they do 3 single tank trips a day so you aren't committed for more then a tank at a time.
Akumal has a serious "water quality" issue. It's not a marine park or mpa, which was the communities choice to not go that direction in the early 90s. While there are many people there who "do the right thing" and put in every effort to promote sustainability and conservation, the resort development in the immediate area, as well as lack of any marine protections, have taken their toll. :depressed:
Where specifically in Akumal are you staying? There's a great shop on Half Moon Bay (that I've used for years), and there are 2 dive shops and one independent dive op running out of Akumal Bay. (I've dived with a couple of them). Who to suggest depends on what's going to be convenient to your location. For cenotes though, I'd go with Diablo Divers.