We stayed at the JW Marriott for 6 days between Christmas and New Years with our 2 teenagers (18 and 16). We actually received an extra night free, so even though the rat for the holiday week was expensive, with the extra night it wasn't too bad. From the time we walked in, every member of the staff was friendly and tried to be accommodating. We arrived at around noon check-in is 4:00), but the front desk people asked us just to have lunch and room should be ready soon. They were spot on, and we were out on the beach by 2:30. So after we checked out, the bell staff stored our luggage and other bags, and we stayed around for most of the day. We were told to use the gym facilities to shower when it was time to leave, and that worked out well. Overall it was a great, relaxing stay for us. It might be a little quiet for families with very young kids, but there were lots of them around the pools, and they seemed to be having fun. Would definitely recommend the JW if Cancun is your destination. A few specifies will follow:
Staff: Doormen were great - we didn't rent a car, so we needed a few taxis, and the guys at the door would have a taxi for us in a few moments. They spoke with the drivers and would tell me the cost for the ride (in both pesos and dollars). Housekeeping services went unnoticed, so that means they were doing their job. Rooms were serviced twice a day, and towels and amenities were replaced appropriately.
Beach/pools: We went to the beach every day, and never had any problems finding chairs or an umbrella. DID NOT have to go down to the beach at 6:00 AM to reserve seats, like at so many other Caribbean/Mexican resorts during holiday weeks. Wait staff on the beach were great; by the second day they knew us by name, and would bring us bottles of water, knowing that we would want them. Constantly checked if we wanted more drinks or food, and delivered it all pretty quickly. They also warned us of which areas in the water had less rocks or coral or stronger undertow. Pool area was beautiful, but pools are not as large as you might think from looking at the pictures. Some of the water is decorative, and not for swimming.
Food: Breakfast buffet is at the Sedona Grill and was very good. Probably 10 fresh juices to choose from, as well as pastries, fruits, omelet station, hot foods, and some Mexican and Asian stations (all at breakfast). There is also a deli counter in the sundry shop with donuts or pastries and a few sandwich selections, if a you want a break or a big buffet breakfast is not your thing. We also went to Gustino for dinner one night, and it was really terrific. The lobby bar was also nice for a relaxing drink or dessert.
Gym/Spa: Very well equipped modern place to work out. There was usualy a crowd, but there was always some machine available. You may need to use an elliptical machine instead of an exercise bike or treadmill, but relax - its vacation and little cross training is good for you anyway. The indor pool and hot tub are very relaxing, and we would unwind there in the late afternoon after being out in the sun all day. There are no little kids at the indoor pool so it is quiet.