Just returned from a two-day conference at this lovely hotel and it is a real stand-out, even by JW Marriott standards. My room (2617) was very large, with luxurious carpeting, sumptuous bedding and plush towels. Amenities were the high-end Aromatherapy brand, generously-sized and with lovely scents of rosemary, lavender and ylang-ylang. There was a fancy illy espresso maker (which I did not use), little Biscotti cookies and the turn-down service brought lovely little dark chocolates (and bottles of water). The bathroom came equipped with a mirror-embedded TV, which was a great idea in theory but I quickly learned did not sync with the bedroom's monitor, so having both on simultaneously as I moved about was somewhat disorienting (however I am probably the minority in this).
One can indicate that a room is to be made up, or that one would like privacy, by pressing a switch right inside the door, allowing a button right outside the room number to glow either green or red. This was a nice touch as I typically manage to sweep the Do Not Disturb signs onto the floor as I walk into and out of hotel rooms.
The hotel provided a Wall Street Journal free of charge, which was another nice touch.
Service was discreet and solicitous, although I did find the front desk to be somewhat understaffed during check-in, and especially during check-out (only two staff were on hand at a busy time while several staff with little to do hung out at the concierge.). I would like to suggest that the hotel considering staffing up a bit more during peak times. Elevators however ran very quickly with minimal wait times.
Food at the conference, and at the Metro Bistro on the 2nd floor, and the more sumptuous db on the first place, was very good. I had to ask for bread three times at the bistro, which I thought was odd, but overall that was a minor point.
All in all an excellent, really top-notch hotel. I would highly recommend the JW Marriott Marquis to anyone whose travels take them to downtown Miami.