bgillis gives a great summary above. We stayed at Iberostar last summer and dove all week with Dressel. The hotel is well kept and well run. The rooms are clean and nice, good sized but not huge. We were a little disappointed with the food. We are not picky and are used to all-inclusive buffet fare. We always found something to eat and some things were very good but the specialty restaurants were disappointing. Breakfast and lunch were fine. I would stick with the main buffet or the steakhouse for dinner.
Dressel did a very good job for us. By paying ahead and considering that Nitrox was included free, I found the cost to be very reasonable. When I decided to add a few more dives they priced it same as my pre-paid rate, rather than full rack rate. The crew were all very friendly and helpful, but they don't carry and set-up your gear (this is fine with me). The boats are not six-packs so you'll see large numbers but they divide off in smaller groups with guides so we had 6-8 persons per group. The dive guides like to keep everyone close but if they learn you are good in the water they give you freedom to roam on your own. It's great to be close to the resort for surface interval to get a break between dives. You can do 1 or 2 dives in the morning and again in the afternoon, whichever you wish, and they just count down the dives you have purchased. Overall, they are one of the best outfits I've experienced as far as positive attitude and a desire to have happy divers. However, if you want to be dropped and left alone, or insist on small (4-6) group size, another boat might be better for you.
I was very happy with both so I plan to return to Iberostar with my friends and will dive with Dressel again. Message me if you have any questions.