A 7 day break with my wife and not knowing the city stuck to a first class hotel brand.
The room we booked looked just a tad tired. Little details like a cheap plastic toilet pan lid surprised me and a couple of other minor points such as a wonky mini bar door.
I understand these are trivial but they are so simple to rectify. A 2 minute repair job. Our external terrace was, frankly, dirty, especially the dividing screen between each room.
Another issue is the lack of a bar of note. The M bar is within the hotel lobby and is poor. Not a bar per se but drinks brought to you from the restaurant into the Hotel lobby.
On a positive note, the staff were excellent and the girls by the pool side couldn't have been more helpful, (Raquel, for example).
All in all a reasonable experience but MO, you need to give the rooms a metaphorical lick of paint.

I arrived at the hotel at 2am still jet lagged from a trip to Asia. I had just been at the original Mandarin in Hong Kong just five days before and immediately felt the same high level of unique service that I received while in Hong Kong. The Mandarin Group has achieved a distinct identity at the high end of the hotel food chain that sets it apart from its competitors. My room was great with an awesome view. The whole place felt very calm and serene. Lunch at the restaurant sitting outside was very nice especially in February and the Asian inspired menu was quite good.
The gym area was nice with a good selection of machines and equip

My husband and I stayed at this hotel recently. He attended a conference, I tagged along for the pool, beach and spa. This property is fantastic for business, only fair for recreation.

The positives: Five-star (impeccable) service throughout the hotel, at the pool, beach and spa; excellent food at the pool-side restaurant (though pricey, but that's expected); our room was very nicely appointed and had a very comfortable mattress, a wonderful supply of pillows and soft sheets; the gym was very well equipped, including non-traditional items such as yoga mats and large exercise balls. There is a lovely path along the water, all the way around the island, to walk and enjoy the kids playing in a nearby park, see the locals walking their dogs and the nannies walking their children. The location is perfect for a conference, and to walk to several excellent restaurants across the causeway. We did not try any restaurants at the property other than the pool-side one, as my husband really wanted to stretch his legs and see something new in the evening.
The negatives: The location for recreation , the "pool" and the "beach." The view from our room and from the "beach" across the water (the hotel is on a man-made island, Brickell Key, in the middle of Biscayne Bay) consists of downtown Miami office buildings and of the busy causeway below. The photos of the pool and the beach on the website were incredibly misleading! The pool was big enough for a dip to cool off, but better left to the birds (literally) as a birdbath (after 5PM, the birds were all on the side of the pool, drinking and washing themselves). I would have gotten dizzy if I had tried to swim laps. The beach has no water access, as the island is built up about 15 feet above sea level, and as there is a fair amount of shipping traffic in the busy bay (there is a port nearby as well). The sand that they imported to a corner of the hotel property is quite lovely, as are the beach chairs and umbrellas, and of course the service continued to be stellar (someone brought me water with ice, and kept refreshing it for me). I just had a hard time again, with the location, the views (skyscrapers) and the fact that the photos were so misleading. Also, the pedicure I received at the spa was decidedly not as good as the ones I get from my local nail spa, and at about five times the price. I hope that my experience was an exception to the rule, but since they had already included the tip on my bill when I went to pay, I didn't have the courage to have them take it off. There was a fair amount of airplane traffic over the hotel at night. We always travel with earplugs, so we were fine.
I researched, with the very helpful concierge, how I could actually get to a real pool and/or beach. The Viceroy Hotel (across the causeway) charges $45 for a pool/spa day pass. Instead, I took her other suggestion: I went to a lovely Kimpton property in Miami Beach (South Beach), with which they have an agreement (I assume) that had both a private beach and a 75-foot pool to do my laps. After a $20 cab ride and about 25 minutes (the traffic was quite bad due to some major street renovations downtown), I arrived and enjoyed my beach/pool day. For about $20 I rented a front-row beach chair, the beach "concierge" brought me breakfast, and I basked in the sun with the sound of the real waves in my ears. My return cab ride was again about 20 minutes and $20. I guess I spent more than I would have at the Viceroy, but at least I got my "real beach" fix.
Finally If you need a cab at a particular time, make sure you "reserve it" because it can be a long wait (at 8:50AM on a Tuesday, it took me 25 minutes to get a cab).
If my husband goes back next year, we may try to stay at another hotel, if it's not too inconvenient for him, but I'd be happy coming back to the Mandarin, now that I know what to expect. We have stayed in other Mandarin Oriental properties, and have always loved them!

Nice rooms, great views, very attentive service and convenient to everything. We had a great "couples massage" and although there is less space to relax and luxuriate that other spas, there was a steam room and sauna. We also enjoyed the huge Sunday brunch that went on forever.