We just returned from a wonderful stay at the old CasaMagna Marriott, now simply called the Marriott Cancun Resort.
It is located next to the JW, so we enjoyed dining at Gustino Italian Restaurant 2 of the 5 nights there! The JW is under renovations right now, so as a family, I was really glad we opted for the Cancun Marriott....much more laid back and family friendly (for ex, the pool at the JW was very quiet and not designed for kids play, compared to next door).
The staff and service was excellent. The wait staff at the pool are rotated, yet they remembered my last name and greeted me formally every day, never making you feel bad if you opted out of an order, but always willing to bring extras, like more cups of ice, for no charge.
The pool menu is good and we ate their almost everyday for lunch. Buffet breakfast has everything you can imagine, at a US premium charge, yet they charge 50% less for kids.
Mikado was a better experience with a Mexican Teppan Yaki chef than the real deal at Desert Springs! He was extremely talented and worked hard to entertain us the entire time he prepared our meal!
We had our 1st meal at Champions Sports Bar and the service was good, but loud music, no windows....not really an Isla Cancun beach experience, so we never returned.
The Caribbean Suite was AWESOME! We had an adjoining room for our children and just loved the wrap around terrace.
The rooms were re-stocked with water bottle every day and although we did order a couple of large bottles for lunch, we never really felt the need to look for a grocery store. The lobby store had all the basics, along with great fresh baked pizza (and at Gold, a 10% discount off all purchases from the store).
We used the Concierge t arrange transpo from the airport to the hotel and that was billed to our room and very nice (brand new van for the 6 of us, w/Cancun Marriott on the side, altho its an outside firm called Prestige). Charges were $16 USD per adult; 8 USD per child under 12. However, we took a taxi (van) back to the airport for under $50 with tip and that worked out just as well.
One thing to remember is the bus takes you into the town on the Isla and it only costs 12 pesos (or a US $1), BUT they will give you a transfer ticket, so your return is free! The busses run constantly, and there are a lot of them! We did not travel at night as we ate 4 nights on the 2 properties and one night we walked about a 1/2 mile (door to door) to a excellent high end Mexican (yet modern designed) restaurant called Porfirio's Porfirio's Cancun Restaurant - Cancun, AGU | OpenTable
Overall, the experience at the Cancun Marriott was excellent and I would return there if my budget allowed me to, next year!