This is by far one of the best adventures I've ever taken. I signed up for the two-day resort course, which included the basic land instructions, pool time, and an open-water dive on the reef approximately 1 mile east of the resort... and this was just the first day. For the second day, I had opted for the two-tank dive trip to Cozumel.
What you get for the cost of your course: instruction (of course), transportation to the dive sites, and use of the equipment. If you wish to use a wet suit, there is an additional charge. If you opt for the Cozumel trip, you also get transportation (by bus and ferry) to the island of Cozumel and lunch after your dives. There's also a little time to do some shopping.
The instructors are friendly and saftey-conscious. The equipment and boats are clean and in very good condition. I've done this trip twice, and both times my experience has been absolutely perfect.
I had heard of other "divers" that have not had the same luck as I, primarily due in part to their sensitivity on the subject of tipping. Many of the top resorts in the Cancun/Riveria Maya area "all-inclusive", and the gratuity is already included in the price of their vacation. Aqua World does NOT share in this gratuity. My basic rule is this: if I had a good time and was treated well, I throw the guys a bone--20 to 50 pesos for a day trip is chump change!
The other complaint that I've heard about is that the instructors were demeaning and rude to the divers. This can happen when a "diver" does something stupid. Diving can be a very dangerous sport! If you're unsafe, expect the tongue-lashing you deserve and say you're sorry.
Once again, I had a great time diving with Aqua World and will be taking their open-water certification course on my next trip to Cancun.