RWB,
I was there in February. I can't say much about operators becaus Scuba Caribe handled diving at the resort we stayed at. They pretty much have the resort dive business.
In Punta Cana itself, the diving is pretty lack luster. The reefs are beat up, there are fish, of course, but anything exotic is pretty rare. Water temps would be in the low 80s now, comfortable in a three mil if you are a cold water diver. The cavern like reefs are a lot of fun to dive and good dive masters can take you in and out of them with ease. Those are my favorite things to dive there.
One interesting point about temps, After about a week, I found I was getting cold in my 1mil suit and started donning a 5mil jacket, especially for the second dive of the day. It is remarkable how quickly cold water divers can become acclimated to the warmer water.
Let's see, my overall experiences with diving there have always been positive. The dive masters and instructors really work hard to make the dive as interesting and fun as possible. There just isn't much there. The one wreck nearby is sort of a joke. Vis is normally pretty good compared to here in Maine. Remember, Punta Cana is technically on the Atlantic side of the island, so you are diving in the Atlantic Ocean.
If you want something a bit more challenging and rewarding, you might try a day trip to Catalina Island. The dive ops can arrange it, and they dive a wall to about 80 feet. Nice boats, very interesting entry, by the way.
There is also a more technical dive operation that has recently opened on the island called Pirates Cove. I haven't been there so I can't comment on it, but I am planning to try them next time I'm in Dominican Republic.
If you are looking for extreme, advanced dives that are challenging, Punta Cana is probably going to be a disappointment. If you are looking for relaxing, touristy dives that will still let you enjoy the amenities of the wonderful nation of Dominican Republic, you will have a great time.
Oh, and Punta Cana is where my ten year old daughter got her certification in February.
Jeff